Just as Paul stated, building your own PC will most likely give you a better price point. I have nothing at all against Mac though, mind you. :)

If you go with this option, you better be prepared to spend some time doing research though. Choosing the right components is cruical for a good and stable performance. When building a new computer, I usually spend around 8-10 hours reading up on components, checking other DAW-setups, e.t.c. Except for some minor glitches with some setups that usually could be remedied with some further research, all my systems have been pretty stable and performed well, at a fair price. My current setup, an i7-920 with 6GB RAM works like a charm, except for a quirk with the USB-devices for which the connections gets lost every now and then (usually no more than once every other week).

Some things to consider, should you go with this option:

• Don't go with the cheapest mother board. A good motherboard is very important for the perfomance and stability of your system. You probably wont be needing support for SLI or tons of PCI-slots though.
  
• Research the motherboard chipset. Some chipsets might cause some glitches for DAW-setups.
• When choosing memory, consult the Qualified Vendor List (QVL) for your motherboard.
• Doublecheck the Motherboard FSB against the clock frequencey of the CPU and RAM-sticks.
  
• If possible, as your system drive, choose SSD.
• Do not underestimate the importance of a good and reliable PSU.

Another challenge is to keep your PC running with as little noise as possible. It does take some research, but if you take the time for it, you'll both learn and get good value for your money. Google is your friend.

 If you are an absolute beginner there are 3 ways:

1 (long, hard but probably the cheapest) learn the computer world (hardware and software) as the music world. You'll never depend on somebody for a life long updatings .

2 find someone who has got programs you like. Ask if he or she has problems of any type. If says no, ask again if the hardware is really ok. If says yes ask if the software is really ok. Then ask again if he or she ever got problems of any type. If he still says "never" is a liar. If he says four to six times in a year, buy the same hardware and software. It has to be the same even in the meaningless particulars. No clones allowed!

3. (the easiest but the most expensive) buy a turn-key system.

  would prefer a Firewire interface with ADAT instead of spdif

 One thing to watch out for on the PC side: it is best to avoid any of the cheap off-the-shelf systems made by Dell, HP, etc.  The real inexpensive PC's of that type most often use cheap parts that while fine for word processing and the like, do not handle the strain of trying to do digital audio very well. 

Also make sure your system has enough hard drives: typically one for programs, one for recording audio files, and one for sample libraries, assuming you will be using one computer.  Again, most of the cheap computers allow for at most only two hard drives.  That limitation will quickly become a real bottleneck.

So is ****intosh a dirty word here?