I'm having a shocking time trying to install SQL Server 2008 on 64-bit Windows 7. When I run setup.exe, I get the following error message:

Microsoft .NET Framework 3.5 installation has failed.

SQL Server 2008 Setup requires .NET Framework 3.5 to be installed

Things I've tried:

• I've checked and double checked. I do have .NET Framework 3.5 installed, with SP1
• I've read about a missing Windows Installer 4.5 installation producing the same error. Win7 comes with Windows Installer 5, which hopefully satisfies this requirement, as I've tried to install 4.5 and it won't let me
• Burning the ISO to DVD and installing from there.
• Installing on an XP machine using the same ISO. This works, so the ISO must be fine.
• Considering SQL Server 2005, but it really needs to be 2008 for the project.
• Update Creating a slipstream version gives the same error
• Update I could install SQL Server Express, and then SP1, but couldn't upgrade to Enterprise.

If you've come across this issue, or know how to fix it, I'd love to know.