I'd stay well clear of VIA chipset motherboards. Also Rage, his memory is 2x512 sticks of DDR, so he can't use his old memory unless we also go with a 4-slot motherboard...
And yes, the DDR/775 motherboards with PCI-E and DDR (non ATI chipset) are usually NOT truly x16 speed supported, but instead x4 speed. While it's a PCI-Ex16 *slot*, it'll only work with cards that can step down to x4 speed while in an x16 slot... which broadly narrows the videocards that can be used!
On the prior page, I'd avoid the NForce chipset also for Intel CPU's. The whole problem you are encountering now is trying to couple an Intel CPU in a 3rd party chipset motherboard. While some work okay, the best performance/match is i9xx chipset for your Pentium D. I also highly recommend Asus + i9xxx chipset mainboards as Asus also tunes the chipset for best performance (i.e. gaming) using Hyperpath and other technologies for memory/latency.
I'm sorry these arent the answers you want to hear... but truly, the whole problem stems from having non-performance/non-intel components on a P4-D.. along with a bizarre mix of components. While it's true you can likely get some improvements in performance, you're only going up a small bit for a LOT of work that way... to mainly save a couple bucks.
If you dont mind staying cramped on Socket 939, perhaps that may be a valid choice... of course, you'll be going with something now superceded but if you dont upgrade very often, it may indeed be the best budget choice/bang for the buck.
OCZ 2x512 (1 gig) DDR400, CAS 2.5 - $92.99 ($84.99 after rebate)
http://www.newegg.com/Product/Product.asp?Item=N82E16820227039
Abit KN8 NForce4 Socket 939 (with 4 ddr400 slots) - $69.99 ($49.99 after rebate)
http://www.newegg.com/Product/Product.asp?Item=N82E16813127221
Athlon 64 3000+ (1.8ghz) - $69
http://www.newegg.com/Product/Product.asp?Item=N82E16819103537
That's a dual-channel/ddr400 motherboard. If you're REALLY strapped for cash, you can hold back on the extra 1 gig and just struggle with BF2 for a while and add another 1 gig down the road (IN PAIRS to keep dual-channel, althought dual-channel's impact on AMD's isn't as great as Intels).