A little information would be helpful:
1) Nvidia or Ati card? Based on the error, I'm assuming ATI. If Ati, you may have to redirect some of the games to another session, which we can show you how to do easily. Or, IF you are not on the livecd and it's actually installed, you can install the newest ATI drivers which have aiglx support and will fix this issue. Are you on the livecd or installed? If installed, did the games work on the livecd?
2) Open konsole, type glxinfo and give us the results. Most important, what do lines 3 and 4 or so say (the direct rendering and video card stuff)? If it says direct rendering is disabled, that would be your problem. You may also want to try glxgears next, and see if it brings up a window with the 3 gears.
3) Is compiz fusion (all the effects) working? If it is, turn it off by right clicking its blue icon in the system tray, and selecting a non-compiz window manager, pref. kwin. Games will often lag with fusion going, sometimes not run at all (but rarely is this the case).