Aside from the dll issue for 2900 users, the bitmap issue is very elusive...
I too am encountering this, have downloaded this thing from three different mirrors, yet always get the same error with precisely the same information. 3dmark06 installs fine, and after renaming the dll in system32/futuremark/etc.etc. it will make it past the splash screen, but then the invalid bitmap file format error. The first time this error occurs, it states this:
Second and subsequent times, it's just "Invalid bitmap file format." with nothing descriptive like that first time.
It's probably something very unusual, seems to be limited to Vista (32 bit here). I'm on a P35 chipset motherboard with ddr2-1066 memory if that has anything to do with it- might be some strange issue specific to a particular hardware platform on Vista 32.
Hope this helps. :)