With every new SQL version, it seems there are more and more headaches getting it installed, unless you're installing it on a clean OS install. I ran into error after error trying to install on a Vista box that had been upgraded to Windows 7 and had SQL 2005 already installed.

I finally dug up a blog entry that helped me out on Mark Michaelis's blog. It took a bit of digging, so I figured I'd give him a bit of google juice: SQL 2008 install registry issues and uninstall rollback techniques.