"Most have never heard of sample libraries or know what a DAW is."
That´s true. But I think, building a PC für music application is not rocket science.
I. Know what application you want use and see what specification is needed. Usually when you buy a new computer, the performance should be high enough unless you speak about exceptional high end systems. For benchmarking you can easily use the typical test sources like Tom´s hardware etc. If they benchmark processors with number crunching based on a mixture of Adobe photoshop, Prime 95 and and some kind of video rendering, that´s not so much different from sequecer software etc.
II.There are a lot of forum sources regarding special components like motherboards, power supplies, coolers and fans. Here you can also trust in the "Gamer´s World". Or ask your computer shop for a silent system and plan ~100 Euro on top for better hardware in that regime compared to 2 Euro fans and "boxed" CPU coolers.
III. If you use audio hardware like the ones I mentioned before from UAD, Liquid Mix, TC etc. go to their user forum websites before buying anything. There are lots of postings about system configuration, which chipsets work nice and which don´t and so on.
IV When the computer shop finds out, that you are a customer for a system in the mid or higher price range, don´t let them sell you a gamer graphics card. You don´t need that. Instead go for a standard or even low end model ( only make sure, that it offers the monitor connections you need, eventuay dual head for 2 TFTs, HDMI or whatever you like). Make sure that it has PASSIVE cooling.
V. Buy a stable power supply. These days you find lots of garbage statements about 800W power etc. Usually it is not so much about how many Watts you get, but how solid the construction and voltage stability is layouted. If you have two models, on 700W for 40 Euro and one 550W for 80 Euro -> take the more expensive one.
Some vendors also offer power requirement calculations on their website, where you input all the devices, which you plan to connect ( mobo, CPU , fans, HDs, DVD, graphic cards etc) and the calculator lets you know how much power you need. Unless you talk about hardcore gaming with highend crossover double cards, you won´t need more than 600 W in most cases.
For example something like this :
http://www.be-quiet.net/be-quiet.net/index.php?StoryID=17&ProductID=219&websiteLang=de
They also have the "Dark power" series, even more highend, but maybe overkill. Depends on your budget,
In any case, don´t buy the dicount no name china supplies for 30 Euro.