Two installations of Inform?

Last year the hard drive on my laptop died, and while I was able to recover most of the data, most of my installations went bust. Luckily, thanks to my pathological need to install things to the “My Documents” folder, that doesn’t include Inform. But now I really want to get in on the latest, but I want to keep the old installation just in case I want to tinker with my previous projects. Would there be any problems with this set-up?

No.

Note, however, that different versions of Inform will generally share their Extensions folder. If you are using different versions of an extension in your different projects, that may post a problem. (If one of the versions is 6L02 or higher you can override the extensions for a specific project by putting them in the .materials folder.)