Well I have an Advent Laptop: 1.86ghz, 1gb RAM and ATi Xpress 1250 integrated graphics (up to 256mb)
I also have FM2008 just for the lappy, tis great fun

Another couple of old gems you need to have are Worms Armegeddon and Hogs Of War. The latter is a great classic!! Rik Mayall rocks!! Also you have to have Command And Conquer Generals Deluxe Edition.
Trackmania United Forever and Worms 4: Mayhem just about work at low settings/resolutions. Found out that Half Life 2 runs relatively smooth on direct x 6
One game that def isn't worth trying is Battlefield 2, was too choppy for me. Team Fortress 2 wasn't worth it either.
To be honest, the good thing about most games is that they have a demo, so its worth downloading it and trying it out...