Just in case you didn't, make sure you run the install with admin rights. With a big install like this one, it might be worthwhile to run in the "hidden" administrator's account (Cf. Administrator Account
Chances are you did, but this may be the point in the install when it tries to write all the registry keys it needs to run. These errors are woefully under-documented. Even people who work for MS think so (the guys at SysInternals, for example). If all else fails, you might try an install with process monitor running. It will slow things down a bit, no doubt, but you may be able to pinpoint the failure better that way.