Need help upgrading my old (2005) hp media center (m7181.uk)

I recently purchased a Acer Aspire 8920G Gemstone Laptop, the reason i bought it was (1) to replace my desktop, and (2) so i could play the latest games, i've played all the medal of honor's and the call of duties (except 4) which i was playing on the laptop, i also played doom 3 and it's sequel and this was all on my media center 2005, plus many more, to cut a long story short as i've already said i bought the laptop to enable me to play the latest games, well it was 2 weeks old to the day when a sky engineer liked the look of it and went for a closer look and it just so happened that there was half a mug of sweet milky coffee on the left hand side of it which he knocked over the left hand side the keyboard, so that's going back to Acer on monday and now i'm left with a 2005 media center with a ATI Radeon X600 (256MB DDR memory/IO Ports: DVI, VGA, S-VIDEO) which tells me it needs a card with shaders 3 or more, Direct X 10 which obviously i don't have or it would let me play Call of Duty 4, Stalker and that newest Splinter Cell, could anyone advise me on a upgrade on that card, i'm not rich so i was looking between £100 to £130 or possibly a little more.
I hope someone can help, Many Thanks