Ok I made a list a newegg.com and I barely made it under the $600 limit. You will have to reuse your old Ide harddrive and you will need to get ahold of a windows xp operating system which you should already have. Yes the Dell xp that came with your pc will work but you will need a product key that will work. It was kindof hard getting a conroe system under $600 without going over the price. You will have to pay the shipping Fee of course so you didnt say anything about that. Your not going to find these parts parts cheaper anywhere else and its best to buy all the items at one site. The parts are all quality parts and your not going to find better parts for any cheaper, I wouldnt go any cheaper on some of the parts like the mobo because if you go any cheaper than the current mobo I selected its gonna be a Cheapo brand. $90ish for a conroe mobo is really really good and its by Gigabyte and they make quality boards with all the bells and whistles.
I had to choose the ati x1600xt its a great video card for the money and the performance you get from it. You do not need a $400 card and you cannot afford it anyway with your budget.. I like the nvidia 7600gt better by bfg but its $144 and you will be over your budget. The x1600xt will do just fine for what you are wanting to do.
I chose the antec case with the powersupply included because its all you need and they make quality parts. The included 450w powersupply is a truepower power supply so you do not have to worry about a cheapo psu going out on you. You lacked the funds in getting a psu and case seperate because they run more money if you get them seperate. Nothing to worry about on this case.
Antec LifeStyle SONATA II Piano Black Steel ATX Mid Tower Computer Case 450Watt SmartPower 2.0 ATX 12V V2.0 for AMD & Intel systems Power Supply - Retail $89.99http://www.newegg.co...N82E16811129155
SAPPHIRE 100146L Radeon X1600XT 256MB GDDR3 PCI Express x16 CrossFire Supported Video Card - Retail $111.99http://www.newegg.co...N82E16814102657
CORSAIR VALUE SELECT 1GB (2 x 512MB) 240-Pin DDR2 SDRAM DDR2 667 (PC2 5300) System Memory Model VS1GBKIT667D2 - Retail $119.99http://www.newegg.co...N82E16820145568
GIGABYTE GA-945P-S3 Socket T (LGA 775) Intel 945P ATX Intel Motherboard - Retail $90.99http://www.newegg.co...N82E16813128015
Intel Core 2 Duo E6300 Conroe 1.86GHz LGA 775 Processor Model BX80557E6300 - Retail $185.00http://www.newegg.co...N82E16819115005
shipping shouldnt be over $30 with the 3day by ups..just guessing.
anyway thats all that you need, remember that you will have to reuse your old harddrive in your old system and you will need to get an operating system. Remember that almost all of the newer conroe boards only has 1 ide controller so you can only hook up 2 ide devices. One for your ide harddrive and one for a cd rom or dvd burner etc.. The mobo has 4 serial ata hookups for future upgrades of harddrives.. Everything is going towards serial ata now that is why they only put 1 ide controller.
A processor fan is already included with the processor.
If you want more case fans just look on newegg they are really cheap.