If you ever think of upgrading the motherboard (the single weakest component in your sytem) this one would fit the bill nicely
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=1649679&CatId=191
You current board only has 4x AGP and would not be able to take advantage of a high performance 8x AGP video card plus it also comes with an uber cool 3.06Ghz processor.
You can move you existing ram on to this board or put some pc3200 DDR 400Mhz up to 2gigs in it.
One problem though, the OEM windows install disk will be coded for the original motherboard and will not install with this new board installed, a quick download of certain operation systems with bit-torrent can fix this though(wink,wink).
So as I figure it 350 bucks could get you a pretty good command and conquer machine
Power supply 30 bucks
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=609635&CatId=0
motherboard 109.00 -the 50 dollar mail in rebate
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=1649679&CatId=191
videocard 165 -the 30 dollar mail in rebate
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=1779348&CatId=318
DDR 3200 RAM 400Mhz 512Mb 57.00
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=1430963&CatId=1043
30- power supply
109- motherboard
161- videocard
57- RAM
= 357.00
Minus mail in rebates 357.00 - 80.00=287.00
Shipping is very low on orders over 200$
All this stuff is intended to fit into your existing case, a little modification is required to get the powersupply to fit into the micro atx slot but shouldn't be a prob for a car audio guy.
This will get your rig into a much higher performance bracket FOR UBER ****ING FRAG FESTS!! MUHAHAHAHA!!.