I was attempting to install SqlServer 2008 on my Windows 7 laptop (just for the heck of it) and ran into an odd problem. Each time the setup ran everything would pass except that "requires reboot" would show as having failed. I rebooted several times however to no affect. After doing a bit of poking around I found that a registry key was holding me back.
This key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\PendingFileRenameOperations
had the following value: \??\C:\Windows\system32\spool\PRTPROCS\W32X86\1_HPZPPLHN.DLL
I deleted this value and ran setup again. SqlServer 2008 then installed perfectly on my Win7 machine.
*Important: it is recommended to install SP1 with SqlServer 2008.