If you going for a high quality music only computer then it is better to build your own from high quality components, e.g., RAM, HDs, soundcards and so on. The off-the-shelf computers (Dell, Gateway) are excellent affordable general purpose computers. For me they have to many proprietary components, e.g., Audigy Soundcards with modified software. This leaves you hostage to the computer manufacturer for fixes and updates - usually very very very very slow!!!!

So, it depends on your objectives. If you build your own you would save at least the labour costs of building it ($80 - $100). Plus you will gain a better understanding of your computer to assist you in operating and troubling shooting it. Also, you get a computer that more nearly satisfies your music requirements.