[Reggie Fowler]

I remember using OS 9 and rebuilding the desktop (to increase speed).

can you do this under OS X?
if so, how?

[TETENAL]

It was "rebuilding the desktop database". There is no desktop database in Mac OS X, so you can't rebuild it. Something similar is the LaunchServices cache, but deleting it does not speed anything up.

[CharlesS]

^ Well, before it was called rebuilding the desktop database, it actually was once just called rebuilding the desktop. That was way back in System 6, though.

You can delete the LaunchServices caches by going into /Library/Caches, deleting everything that starts with "com.apple.launchservices", and rebooting. However, as TETENAL said, this won't speed anything up (it may actually slow things down a tiny bit as the system has to re-cache all the icons on the system), and it will also reset all your "Open With" settings to the defaults, so you really shouldn't do this unless you're experiencing some sort of problem (examples of problems that could be solved by deleting the LaunchServices cache include icons not displaying properly and documents not opening with the correct application).