GTA could be a possibility, but unless the code is out there (which I don't think it is), it would be a port; and that's a pretty hefty dev project, especially one which RockStar Games would most likely sue the pants off of.

CounterStrike? It's a 220mhz ARM processor. Your Pentium 1 120mhz has more processing power, try installing CStrike on that and see how it runs to give you an idea.