Maybe I missed something but my pro version of Unity 2 has been overwritten when I got Unity 3. 
Just wanted to try Unity 3 before I bought it.
Yeah you need to rename your Unity folder to something else, then install Unity 3 (and then you can rename that folder too). Another thread mentions installing both that way, and I’ve tried it on Windows and so far had no trouble with trialling U3 without it harming 2.6.1 doing it that way. Don’t forget to change the start menu folder name too to keep that from changing as well.
I learned the lesson about Unity arbitrarily overwriting and removing everything when I reinstalled 2.6 over itself to fix something a while ago… lost a ton of packages I’d kept in the same folder as Standard and Pro… ouch!
Thanks. Now I wish I had backups on my mac 
I thought OS X had some default backup thing, time machine or something? I’ve not delved too deep or anything, but you might get lucky and find a way to recover the old stuff? Though if it was just the installation then you can reinstall and good to go again.
You would have to have an external hard drive for time machine, and I would’ve had to set it up before I did this.
Bummer