First off, RAM should be a priority. Get it to at least 2 GB, which shouldn't be too expensive. RAM is cheap these days.
As for a video card, I've been hearing very good things about the Radeon HD 4850. I'd suggest that, it's apparently very good and it can be found for less than 200 USD.
1GB Memory Compatible with Acer Power Kt Sd2.6-LCXPP Sd20-LCXPP Upgrade DDR DIMM, 1GB Memory for Acer Power Kt Sd2.6-LCXPP Sd20-LCXPP 184pin RAM DDR DIMM New, 2GB RAM for Acer Power S290-UC3600C S290-UC3600P S290-UC4200P 240pin Memory DDR2, 2GB RAM for Acer Power S290-EC3520P S290-EC3600C S290-EC3600P DDR2 DIMM Memory, 512MB RAM Compatible with Acer Power Sc10-LCXPH Sx Upgrade SDRAM DIMM Memory, 1GB RAM Compatible with Acer Power SK50 DDR2 DIMM Memory 240pin New, 1GB Memory for Acer Power FH-UP6410P S290 SK30 DDR2 DIMM RAM 240pin New, 1GB KN.1GB01.007 Memory for Acer Power FH-UD4400P FH-UD4401C FH-UD4401P 240pin, 1GB KN.1GB01.007 Memory for Acer Power FH-SP9250P FH-UD2160C FH-UD2160P DDR2, 1GB KN.1GB01.007 Memory for Acer Power FH-FP9150C FH-FP9250P FH-SD2140P DDR2, 1GB RAM for Acer Power FH-FP6310P FH-FP6410P FH-FP8200P 240pin Memory, 1GB RAM for Acer Power FH-EP9250C FH-EP9250P FH-FC3520C Upgrade DDR2 DIMM Memory, KN.1GB01.007 1GB Memory Upgrade RAM Compatible with Acer Power FH-EP6311C, 75.063A3.G01 1GB Memory Upgrade RAM for Acer Power F6-SP5241P F6-SP6310L, 75.063A3.G01 1GB Memory Upgrade RAM Compatible with Acer Power F3 F6 F6-SC3460L, 1GB Memory for Acer Power 2000-UD6321C 2000-UP651C 2000-UP651P 240pin RAM DDR2, 1GB Memory for Acer Power 2000-UD431C 2000-UD4401C 2000-UD6320P DDR2 DIMM, 1GB RAM Compatible with Acer Power F5 M8 DDR2 DIMM Upgrade Memory 240pin New, KN.51202.012 512MB Memory Upgrade RAM for Acer Power FV M6 S210 DDR DIMM 184pin, 1GB Memory Compatible with Acer Power S285 184pin RAM DDR DIMM New, 1GB 184pin for Acer Power FV M6 S220 Upgrade Memory RAM DDR DIMM New, 1GB Memory RAM Compatible with Acer Power F1b F1c FV DDR DIMM 184pin New, 1GB Memory for Acer Power SK20 184pin RAM DDR DIMM New, 1GB Memory Upgrade RAM for Acer Power Kt Sd2.6-LCXPP Sd20-LCXPP DDR DIMM 184pin, 1GB RAM for Acer Power Kt Sd2.6-LCXPP Sd20-LCXPP DDR DIMM Upgrade Memory 184pin, 1GB RAM for Acer Power S285 184pin Memory DDR DIMM New, 1GB Memory for Acer Power FH-UD4401P FH-UP6410P S290 SK30 240pin RAM DDR2 DIMM, 1GB Memory KN.1GB02.008 for Acer Power F1c FV Special M6 184pin RAM DDR DIMM New, 1GB DDR DIMM for Acer Power SK20 Upgrade Memory RAM 184pin New, 1GB Memory for Acer Power FH-UD4401C FH-UD4401P FH-UP6410P S290 DDR2 DIMM RAM, KN.1GB01.007 1GB Memory Compatible with Acer Power FH-FP5240P FH-FP6310C, 1GB KN.1GB01.007 Memory Compatible with Acer Power FH-EP9250C FH-EP9250P, 1GB KN.1GB01.007 Memory RAM for Acer Power FH-EP6310P FH-EP6311C FH-EP8200P, 1GB KN.1GB01.007 Memory Compatible with Acer Power F6-SP9450P FH-EC3520C, 75.063A3.G01 1GB Memory Upgrade RAM Compatible with Acer Power F6-SP5241P, 1GB DDR DIMM for Acer Power F1b F1c FV Special RAM Memory 184pin New, 1GB Memory for Acer AcerPower APFH-EC3520P 240pin RAM DDR2 DIMM New, 1GB Memory Upgrade RAM for Acer AcerPower 1000 DDR2 SO-DIMM 200pin New, 1GB Memory RAM Compatible with Acer AcerPower F2 184pin DDR DIMM New, 1GB Kit (2x512MB) Memory RAM Upgrade for Acer Acerpower SP Series, 512MB Memory RAM Upgrade for Acer Acerpower F2 DDR 333MHz, 2GB Kit (2x1GB) Memory RAM Upgrade for Acer Acerpower S280 Series, 2GB Kit (2x1GB) Memory RAM Upgrade for Acer Acerpower S260 Series, 1GB Memory RAM Upgrade for Acer Acerpower F2 DDR 266MHz, 1GB Memory RAM Upgrade for Acer Acerpower FG-U Series DDR2 533M, 1GB Kit (2x512MB) Memory RAM Upgrade for Acer Acerpower ST Series, 2GB Kit (2x1GB) Memory RAM Upgrade for Acer Acerpower F5, 2GB Kit (2x1GB) Memory RAM Upgrade for Acer Acerpower Power FE, 1GB Memory RAM Upgrade for Acer Acerpower S285 Series DDR 333MH, 1GB Memory RAM Upgrade for Acer Acerpower SD Series DDR 266MHz,
