I've never had SQL Server running on any of my clean installs of Win7. Are you sure you didn't install any Windows Live programs or are using a branded OEM installation DVD like from Dell? The branded OEM install discs I've seen do have Windows Live preinstalled and they apparently need SQL Server. Uninstalling the Windows Live programs gets rid of SQL Server on reboot.
MS-MVP - Elephant Boy Computers - Don't Panic!