oi... that's old. most modern (even low end) gpus will be severely bottlenecked by that system. It's an AM2 right? what's your motherboard? it might be ideal to upgrade the cpu to a first gen PhII if possible. (depends on the motherboard)
as for gpus... they're price has been crashing down recently... you can get a HD7750 for like $70-$80, which would be more gpu then you need.
grab a 7750 or 650 you can get them for almost nothing. and they shouldn't be too handicapped by your cpu.
see if you can't hunt down a Athlon x2 6000+, your mb should support it... and you'll see a modest boost in performance. (probably get one off EBAY for like $30)
what about GT610 2GB ? its 40 euros
terrible advice. That's for web browsing or using Excel... it's not a gaming gpu. furthermore that gpu isn't even close to strong enough to use half a gig of memory, he doesn't need a 2gb of memory on that cheap workstation card. A 650/7750 will be rather cheap (their price has fallen like a rock this month) and give him a significant boost in gaming (don't bother getting a 2gb version of either card)