The BGE has a check that keeps ATI cards from using Vertex Arrays with Display Lists. Instead (if Display Lists are enabled), the BGE will use Immediate Mode for rendering, which is rather slow.
I have uploaded a Win32 build here, and a Linux 32 build here. I don’t have an ATI card, so I can’t test this. So, could users with ATI cards test this build on some of their scenes and report back any differences (good or bad) between regular Blender and this build? Also, please post what graphics card you’re using (e.g., HD 2600).