>Not positive, but it may be that SQL Enterprise will only install on a server OS. I know the developer version will install on XP though.

I have an image of my PC. So, it is the same OS. Here, the problem is the SQL Express that has been installed with Visual Studio 2008. Because that version is newer, the install of SQL Server 2005 is blocked. So, I tried to uninstall SQL Express but I just can't find how to achieve that.