If you willing to do a pretty easy OC, than try these two out and save the $ for a good GPU or upgrade to Penryn later when you want another boost in performance.
CPU - $80 shipped e2160
http://www.mwave.com/mwave/skusearch.hmx?&scriteria=BA23881
Mobo - $98 shipped - $20 MIR (if you trust MIR’s) = $78 Hard to beat at this price.
ABIT IP35-E INTEL P35 CHIPSET ATX FORM FACTOR 1xPCI-E(X16)/2xPCI-E(X1)/3xPCI/4xDDR2 W/SATA2,LAN(Gb),USB 2.0 & AUDIO
http://www.mwave.com/mwave/skusearch.hmx?&scriteria=BA23929
Linkage for OC done by Tom's:
http://www.tomshardware.com/2007/09/12/pentium_dual_core/
Here's some RAM links and prices, if you need them:
Memory - $102 shipped - $40 MIR = $62!! Solid performing CAS 4 DDR2
CORSAIR XMS2 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory – Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16820145034
Memory - $110 shipped - $47 MIR = $63!! Good OC’ing RAM + CAS 4 too.
Crucial Ballistix 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory – Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16820146565
Memory - $93 shipped - $30 MIR = $63!! CAS 4 and good RAM
GeIL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16820144062
And if you need a newer PSU, this one will do just about anything for a single card GPU!
PSU - $100 shipped - $45 MIR = $55!! can’t beat for this price
Antec NeoPower NeoHE 550 ATX12V 550W Power Supply 100 - 240 V UL, CUL, TUV, CE, FCC, CCC, CB, C-tick – Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16817103941