Well first things first: If youre not looking to spend a lot, Intel CPUs and NVidia GFX are out of the question.
An AMD Athlon XP 1800 runs at 1.53 ghz, only costs $50.
An ATi Radeon 8500 will run around $70.
PC2100 DDR Ram 256mb - $31, 512mb - $64.
60gb Western Digital Hard Drive - $55.
Asus A7S333 Mobo - $55
Soundblaster Audigy - $50 (optional, mobo has built in sound, but audigy is much nicer)
Ethernet card - $10 (only if you use broadband)
Lite-On 40x10x40 cdrecorder - $31
Samsung 48x cdrom - $17 (only need it if you want to do direct cd-to-cd copies w/o copying to hard drive first)
case - $20-30 for a cheap generic one, $50-100 for a nice one
add that up and see if you like the price
there's still some other things (cables, keyboard, mouse, speaks) but that stuff doesn't cost too much, and you could always use your current ones if ya wanted.