The question's a bit rhetorical as far as Windows is concerned, because I don't think you can install IE6 on Vista, and you have to have XPSP2 to install IE7, where IE6 is installed as part of the OS. So, if you're on XPSP2 and have installed IE7, they are both installed. If you uninstall IE7, IE6 should reappear by magic. Now, running them concurrently or separately is a different matter, but it should be possible with some judicious partitioning. Noel