I have the same problem, I tried to explain this in other italian forums but I didn't have an answer. One week ago I tried my experiments with Joomla templates, I modified templateDetails.xml and I had a crash. Not only Joomla was unable to respond, but even phpMyAdmin fails showing an error window with this message:
Can't create/write to file '/var/folders/hy/_7b1fpjx3fv31psr2wtwv04h0000gn/T/#sql106_6_4.MYI' (Errcode: 13)
I tried to uninstall/reinstall xampp several times, but was the same story: installation OK, phpMyAdmin works; installation of Joomla 2.5 or 3.0 (both gave errors), OK; all OK? Not at all! Shutdown/Startup of xampp MySQL server and the blocking message error reappears. No way to eliminate it. Joomla 2.5 gave the same errors of the previous installation (?!!). And the new PHPMYADMIN remembers the names of the old databases. So it's not true a new installation erase completely the old one. So I think anything in ~/Library folder, I found a folder ApacheFriends, I erase the content, I restart with another installation... the same old story. Now I have a Mac XAMPP without problems, but only if I don't try to install Joomla. I'm astonished. Where Xampp saves the state of the previous instances?!? The old database names, the old Joomla errors, Errcode 13 blocks everything.
Anyone can help? I don't want to abandon my Mac with Dreaweaver and return to WinXAMPP/Notepad++.