Well, step one is to go to the root (top) level in the finder. Perhaps it's just not showing the drive on the desktop but it is still accessible in the finder? Open any finder window, Apple-2 to go to list mode, then apple up-arrow repeatedly until you are at the top. See it?
If not, then step two will be to open Applications > Utilities > Disk Utility and see if it shows up on the left side as plugged in or mounted.
If it doesn't show up there, try testing it on another mac to see if it's your firewire cable or port.
Any luck?
edit: I guess it's called Command-2 then Command-up-arrow.