The boot drive's format and partition structure can be checked both in the OS X graphical interface and in the Terminal.
If your system hangs when going into Safe Mode, or will not load into Safe Mode at all, there are a couple of things you can do to fix the situation.
There are several common ways people can verify file system integrity in OS X, including booting to Safe Mode, using Disk Utility, or running the 'fsck' tool. These options have had some people wondering which is best.
Troubleshooting Mac OS X 10.2.2: Norton update sees disks
Troubleshooting Mac OS X 10.2.1: Smith Micro on FaxSTF delay; Norton Utilities error reporting; more
A number of Snow Leopard users have run into a problem where upon backing up with Time Machine they get an error "109" claiming the backup disk image could not be accessed. Here's a possible solution for this.
Troubleshooting Mac OS X 10.2.8: Apple may provide new batteries to some users; AirPort Base Station problems; more
Special Report: Troubleshooting Mac OS X 10.2.2