OS X disk first aid hangs

You should try the standard troubleshooting suggestions:
http://www.apple.com/support/mac101/ (see the "My Mac needs help" section)
http://www.macosxhints.com/article.php?story=2004011205473937
http://forums.osxfaq.com/viewtopic.php?t=7269
http://www.thexlab.com/faqs/faqs.html

In particular, be sure to try logging in as a different user to see if the problem exists there. (Create a new user via the Accounts preference panel if you only have the one user account so far.)

Also be sure to do both permission repair and filesystem repair.
http://docs.info.apple.com/article.html?artnum=25751
http://docs.info.apple.com/article.html?artnum=106214

Do you have any external firewire drives attached to the system? and are they turned on and mounted when you try Disc utility? If they are not, turn them on and try it again....

I experience a similar issue (not all the time) and that does the trick for me....