Don't go cheap on the RAM!!! You will hate yourself later, especially if it is a no-name brand. Also, Go with a decent motherboard with extra options. I will give you a list of my PC and I only paid around $1000 for it. Minus the Hard Drives and Video Cards, which I already had or bought at a later date.
AMD Athlon XP 2500+ Mobile (excellent for overclocking)
Abit AN7 Motherboard (Nvidia NForce Chipset, no need for audio card)
Thermaltake Xaser III Case with Harcano System and 7 cooling fans
Thermaltake Volcano 11+ Heat Sink and Fan
Antec Truepower 550W Power Supply
OCZ Enhanced Latency Platinum Edition Memory PC3200 (2X512MB)
Plextor DVD+/- RW Drive
Lite-On DVD-Rom Drive
Cheap Sony Floppy Drive
I bought a Geforce 6800 Ultra after the fact, and also a 200GB SATA Hard Drive and a 300GB SATA hard drive.
Make sure your motherboard is SATA ready. The days of the IDE Cables are slowly phasing themselves out.
Also, you will need some good thermal paste to put on the CPU. The stuff that ships with them are crap. I would go with Arctic Silver 5 or better.
Lastly, if you aren't too stuck on the 64Bit stuff, I would discourage it. You can better spend your money in a lower priced Athlon and overclock slightly and have a PC that runs just as fast. Athlon is the best CPU I have found, because of their architecture and the way they process. For instance, I bought an Athlon XP 2500+Mobile that is a 1.83Ghz CPU. I easily overclocked it to 2.4Ghz without any issues and have had it there since July 2004. My temps are constantly at 30 to 35 Celsius. Also, it was only $89 so if I fry it, I can afford another.