I just asked myself the same Question an I tried OpenTTD and Civ 3.
OpenTTD workin without any Problems, but Civ 3 is not working properly.. It's like two little Game windows side by side, both in black n white an you can't really see things goin on. Only the Buttons in the Menus, so you can click on 'Exit'
(How) Can I install OpenGL afterwards? And how can I see if it's working? I can't remember for a point in the system profiler telling 'OpenGL: xxxxx'?! I gotta check that when I'm on my hackbook later.