When you think you are done with the development, you are at the beginning of resolving cross-IE compatibility issues. At least as a beginner every one of us have gone through this phase. The world is offering IE Collection, IETester, Multiple IEs…
Maybe it’s not a definitive answer, but I’m glad that someone confirms my impression that all these are not perfectly relevant: http://stackoverflow.com/questions/2537885/is-ie-collection-reliable-tool-for-testing-with-various-versions-of-internet-expl
And finally, although it’s limited to windows (it’d be too much to run genuine IE without windows) this solution works for me: http://www.microsoft.com/downloads/en/details.aspx?FamilyID=21eabb90-958f-4b64-b5f1-73d0a413c8ef&displaylang=en
The point is that – one single windows license is enough (xp, vista or 7) and you can run the Virtual PC downloaded from the link above, and it should be the same setup as the real people’s windows/IE.
I’m still wondering if it’s possible to run Virtual PC in VirtualBox Windows guest on Linux VirtualBox host machine. I’ll update if I ever come across an answer to that.