There's a registry key you can set to prevent the install of IE 7.0:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\7.0]
"DoNotAllowIE70"="1"
Save this as a .reg file, double-click, and you're done. If you want to undo this setting, either change the '1' to a '0' and re-run, or delete the key from the registry.
I've successfully used this myself.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\7.0]
"DoNotAllowIE70"="1"
Save this as a .reg file, double-click, and you're done. If you want to undo this setting, either change the '1' to a '0' and re-run, or delete the key from the registry.
I've successfully used this myself.