The four SE libraries will fit comfortably in 8 gigs of ram.  You would probably be ok using just the four SE libraries and your sequencer on a current laptop (note the word "probably").  However, once you start adding Vienna Suite, VE Pro, VI Pro, etc., you will quickly need 12 gigs.  As it sounds like you will be eventually looking to add full collections (from your comment regarding "big"), there is no way that will run on an existing laptop as has already been mentioned.  Once you start trying to go "big" you will likely quickly find a need for 24 gigs or ram, and a much faster processor.  "Small" can be done on a laptop.  "Big" still requires a desktop.  Those who seek to do "really big" tend to end up either with multiple computers or one computer often with a dual xeon processor and 48 gigs of ram (way out of my budget btw).

As Cyril mentioned, the forthcoming VE Pro coupled with an SSD drive may change things considerably.

Appassionata + SE PLUS needs 12 or 14 GB (if my memory is good)

All that depends of how many articulations are loaded per instrument

Look at my configuration : I can load all the articulations of what I own but I need a VM file of 3 GB ; could be risky

If you are only loading a couple of patches for each instrument relatively little memory is required.  However, to achieve greater realism, many patches are helpful as each instrument is capable of many articulations.  Good instrumentalists will use all of them when playing.  Good players will actually use many subtle variations of each, more detail than sample libraries can provide, though with the many articulations provided in the full libraries, IMO VSL comes closer to "actual" than any other library.

In my own templates - and I have only a few of the full libraries along with the SE libraries (and MIR SE) - my 12 gigs of ram is barely enough for what I am seeking to do.

Without more detailed information, that is a question that really cannot be answered (and not one that I would really be qualified to answer).  For that question to be answered - and the extent to which a laptop may work for you - it would be important to know many more details about how you plan to use VSL in a live situation.  "Big" as initially stated implies problems - hence our responses, while "a couple of backing tracks" would likely work.

Note also that problems exist with using a new laptop.  The biggest is that firewire audio interfaces generally do not work well - the type of firewire chips commonly used are known bad things.  If you really have to use a laptop, and have a good sized budget, it would well be worth finding a company that specializes in building computers for use with VSL, and laptopls in particular, and purchasing from someone on that list.  VSL does suggest a couple of vendors, but the address of that page escapes me at the moment.

what does it stop you using a desktop on stage !

it's smaller than a guitar amps !

You can rack it ! 

You can use an Ipad to control it !

i didn't know that firewire can be complicated with laptops!!! what aboiut if i connected my audio driver via USB, or even USB 3?

Cyril, what's stopping me is that this live performance is going to be every week, yes, every single week, now it will start at 7 pm, i finish my job at 5 pm, so ihave 2 hours to get to my home, change my cloth, eat something, unplug the desktop, g to the place, plug the desktop, test the devie and hmmmm what do i forgot....... breathing [:D][:D]

that's why i'm tinkng about getting a laptop [:)]

the problem is that i can't estimate how a processor will act from reading its sspecifications [:S]

i'll try to bring some info about mainstream laptops that i have in my market and le's see what works best, if it will work!

i really appreciate your help folks, thanks a lot

Be aware that "main stream" laptops can tend to cause problems as they often use cheaper components that sometimes do not deal well with the high stress loads of DAW use.

USB can work as an interface, though other options are generally better.  One company, RME, does produce very highly regarded USB interfaces, but those are not cheap.  They are known for good drivers, and for live stage use, having something that rock solid could be a plus.

As stated before, I would urge you to contact a company that specializes in computers for music production/performance.

Another option, though not one I know much of anything about, would be to get something along the line of a portable cube computer.  A DAW maker might very well offer something that would be robust enough, for less money than a laptop, and then you could add a dedicated LCD monitor.

It would also be a good idea to continue to do more research before purchasing anything.  The last thing you need is to discover all kinds of major problems - that perhaps cannot be fixed - after your purchase.  For casual/hobby use one can manage to use all kinds of non-optimal equipment.  For what you are going to be doing, you will not have that sort of error margin.  You need something that will do what you need, and work well.

Unfortunately, the only companies I know of or have dealt with are in the US, and that will likely not be of help to you.  The one I have purchased from in the past is ADK, and they do offer a specialized laptop.

noldar12 thanks for your warning and advice, the problem is.... as i know, there's no special copmanies in selling laptops for music here in Syria and i don't know if i can find a cube computer

and probably the only availabe are the mainstream laptops !! looks like i'm gonna end up with a deskop after all ....

i'll continue researching and get back to you guys

Look at the "refurb" on Apple site, you can get 20 % off 

http://store.apple.com/us/browse/home/specialdeals/mac/mac_pro?mco=MjEwNzM3NTk

This is the refurb of US, you must select yours [;)]

all this depends of how many articulations you are going to load in memory

@davidl466 said:

I do realize that Cyril...but since I don't know how much memory each articulation takes up I can't really tell. Looks like you have a pretty big setup as far as RAM goes and probably have no problems. My biggest thing is that it would be nice to just upgrade my OS to 10.6 to be able to utilize all my RAM rather than build a slave PC, of course, IF my Mac Pro will be able to handle all the samples easily. Again, the only reason I was going to build a PC slave is because Hollywood Strings uses a TON of RAM and I guess doesn't work nearly as well on Mac as it does on PC...and since VSL uses so much less memory and is a bit more optimized for Mac (I think)...anyway, those are my concerns David

AFAIK OSX has been 64bit since Tiger. In any case, SE can be loaded into around 4GB, so you should have plenty for that.

DG

In the documentation of each VSL instrument it give you the size of what you are going to load

You can work with VSL in 2 ways

1) you build your orchestra as you are writing your song

2) You have your whole orchestra with all it's articulations loaded into memory and you write your song (my choice)

In case 2 you nead a lot of memory, in my setup I need 28 GB (24 GB of RAM and 4 GB of swap used)