I have CS5.5 Master Suite running on Windows 7 at work and at home. I'm changing to a Mac at home. Can I download CS5.5 for the Mac at home and use the same license? I can't deactivate the home computer because my system died. Hence the moving to a Mac.
No. The best bet for you is Creative Cloud which allows two installs and activation but they can be mixed platform.
Also of note, even if you were only switching platforms on both you’d still have to go to CS6.
Adobe only does platform swaps on current versions.
Finally, if you have to stick with CS5.5 you can always install Windows on the Mac and run it that way.