You can verify—but NOT repair—your directory using Disk Utility if you have booted from the volume you wish to repair. Most users elect to run Disk Utility from a Mac OS X install or upgrade DVD for that reason.
You might instead install
applejack, a shell for unix routines in Mac OS X, which you can boot into using your boot volume—once the utility has been installed—and repair you direction, repair disk permissions, empty cache files, validate preference files and delete unneeded virtual memory files. You can find that open source utility
here.