Software update won't finish

I just installed Snow Leapord on my 2007 iMac a few days ago. That installed just fine.

My browser wasn't loading an important webpage so I ran a System Update. (Safari, iTunes, Security, etc.)

It took forever to update and when the blue bar reached the very end it never finished. I left it all night and it is still there (not frozen) not ending.

Could it possibly be still installing the update after 9 hours?

Is it dangerous to restart? Do I have any other choice?

Thanks in advance.