Do you want to use an older version of IE on Windows 7? You cannot install an older version natively; you have to use IE8. Compatibility mode may fix most things but there’s possibly that LOB application that won’t play nice. You can do things like get the app vendors to update it (maybe they are gone, maybe it takes too long, or will cost too much). You can run an older generation OS on Terminal Services.
However, a tidy way to do it is to use XP Mode and use the older versions of IE that will run on XP. The shortcut can be published to the Windows 7 start menu to make it easy to use for the end user. We showed this and explained this scenario in some of the Windows 7/Server 2008 R2 launch events in Ireland. I put it together at the last second in the Dublin events as one of the speakers talked about the scenario … yeah we were that “seat of the pants” and we reacted to questions being asked. Flexibility rules.
Ben Armstrong (product manager AKA the Virtual PC Guy) blogged how to do this. It is very easy.