You can build a computer using exisiting box, HD, power supply, CD, floppy, ethernet card, modem, that 9800 ati card etc, for about $130. Or.....you can pay $550 for the new one that will be bascially the same as what you can build. Take a look either on the inet or through fryes and you can buy the MB/CPU combo but you will still need to spend around $50 for the ram.
You get all the drivers you need for the MB when you buy it and can dl the latest updates. Xp will do it all for you....
I upgrade MB/CPU/Ram about once a year.
Hope this helps..