Well I was browsing through the download site softpedia.com and I was surprised that they have the IE 7 beta available. If this is legal or not I have no clue. I didnt download it just because I'm not sure if it will overwrite IE 6 and if it does I do not know how stable it is. Anyway if your just itching to try out IE 7 here is where to get it.
Who knows if it's legal, it was leaked out of the test group. I wouldn't download any MS software that is so intertwined with the OS from any website even if it's a trusted download service or not, I'd only use Microsoft Downloads, Microsoft Update, or Windows Update. More than likely it will install over IE6, therefore for system stability avoid it until it's finalized and is made available from Microsoft Downloads, Microsoft Update, or Windows Update.
There's also some discussion about it here, on a different forum.
Knowing MS I wouldn't doubt if there's some remnants left over in the registry, and even possibly on the disk. To say a restore point isn't needed you'd have to use a program to watch the installation (InCtrl5, System Mehanic, Total Uninstall, etc.), and then compare the results after removal.
It seems microsoft found out about Softpedia hosting IE 7. This is now written above the description:
Because this version of Internet Explorer 7 is intended only for developers and registered beta testers, Microsoft has asked us to stop distributing the setup files. Therefore, Internet Explorer 7 is no longer available for download from this page.
However, we will post it here as soon as the beta goes public, so make sure you periodically check back.