Okie doke...
Firstly Jeiss, it really isn't that difficult to build your own PC. All it takes is a bit of time and effort to research what are the best components and which ones work together. Building your own computer will also give you the choice of what type it should be, and how upgradable you want it to be. In my experience a high end ready-made PC will cost less than a hand built high end PC, but the hand built one will have higher quality components, will last longer and be more upgradable.
I've just fixed a few friends computers, and I have to say the stuff I saw inside thos eboxes made me cringe. I am never going to buy a pre-made computer ever again. Build and component quality is frequently awful.
OK, so lets assume you can't be arsed anyway - what should you buy?
Firstly, what do you want your computer for? If it's mainly for games, then I'm sorry, but the graphics card is far more important than the processor - a high end P3 or Athlon (1 GHz or over) will do you well for the next two years (unless this trend of "oh look, a new game as come out this month, time to upgrade again" continues). But RTCW runs very nicely on my 1GHz P3 with my ancient TNT2 (albeit overclocked).
Athlon or Pentium? As far as old-gen goes, the Athlon beat the P3 trousers down. The newer faster P4's (2 GHz+)have a slight edge on the Athlon XP's, but the XP is better optimised for doing stuff that operating systems and games do, plus the faster P4's run even hotter than Athlon XP's. If I were you, I'd get a processor like a XP 1800.
It's not just personal preference. The Athlon architecture is better designed than the pentium families, meaning they give the same performance at lower clock speeds. However, the pentium chips are much faster, so at the moment they can just about outstrip the Athlon XP's, but like I said they run damned hot.
Don't be fooled into making a dual processor system. Yes, I want one, because my OS (Linux) and most of it's programs support dual processor architecture. Virtually no ordinary windows program I can think of has dual processot support - meaning that although your computer has 2 CPU's, it's only ever going to use one of them. Obviously, if you're a graphic designer and you demand that 3D Studio Max and PhotoShop run faster, fine, but in your case - don't bother. Dual processor architecture is made for servers and/or machines that do alot of very CPU intensive tasks (such as MPEG encoding).
As far as graphics cards go, I know sod all about them really. I don't care much for fancy visuals, and I would rather pay for a card with features I want (such as multi-monitor output, video in/out - such as
this Gainward card.
Buy lots of memory. 256 MB is too small to run Windows reliably and quickly if you tend to us elots of programs at once like I do. Go for 512 MB. Going over 700 MB is too much.
USB 2 support may well become "essential" for many people (although not for me, as the only USB device I own is a zip drive). It's data trasnfer peed is comparable with firewire, but obviously most digital video cameras don't come with USB 2 ports, so if you're looking to do lots of video editing you'll still want a firewire. If you want lots of external stuff (USB printers, scanners, hard drives etc) then I'd say USB 2 is a must.
I know sod-all about American OEM's, so I guess you'll have to take everyone elses word on it...