Just build a new computer.

You can buy a Soyo KT600 Motherboard with SATA Raid and a AMD XP CPU all for less than $100. Then pay $50 for a decent graphic card. $90 for some very nice PC3200 512Mbytes ram. $70 a 80G Western Digital 8MB-cache harddrive. $8 for a floppy drive. $80 for a 8X DVD-RW Drive. You can use the motherboard built-in sound chip for sound because it is not bad unless you're an audiophile. That is $398 excluding tax. computer case you can spend anywhere between $30 to $80. I recommend getting a $50 Enermax case because it has decent powersupply and looks good.
If you're cheap, you can cut down the cost drastically by buying a $50 motherboard with an integrated graphic chip. Choose cheaper PC2700 ram for $70. Buy a combo CDRW drive with DVD reading capability for $40. This will cut down the total cost by $100. Of course, you will have a system that is slower and has less features.