1. Start regedit.exe

2. Create the following key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Setup\7.0

3. Click the Edit menu and select New and then DWORD value.

4. Name this new DWORD: DoNotAllowIE70

5. Set the value of this DWORD to a value of 1.

You can also download Microsoft's IE7 Blocker Toolkit as another option.