Yes, I also have SU 6 installed (and separately licensed). Then I also have SU 7.0 and 7.1 separately installed, too (although their licensing is not separate). So you can have a whole bunch of versions installed separately and you can even run them together if you wish.
Note that if you double click on an skp file (and launch SU this way) it will always try to launch the version you saved anything in last.
Also note that while you can open SU 6 files in SU 7 (and even "save as..." a v.6 file), you cannot open a v.7 file in SU 6.
I think that's all.