Moodle is just php code that uses MySQL as DB backend and Apache to serve it out. What's described here is an XAMP issue ... not Moodle. From Googling, EXC_BAD_ACCESS (SIGSEGV) can see that this error is not restricted to Moodle installs, but a variety of apps on a Mac - MS Word, Adobe, Final Cut Pro, for examples.
Since you've not really begun anything, think I'd start by un-installing XAMP. Then check your operating system for issues. Could be your HD is need of repair.
Have another user on that Mac that's allowed to admin it? Login as that user. Install XAMP and see what happens.
If you don't think that's the issue, suggest posting the issue over at XAMP forums:
http://www.apachefriends.org/f/viewforum.php?f=29
'spirit of sharing', Ken