Click the apple icon in the top of the task bar (opposite end of the clock, blue apple).
Select "force quit"
OR just hit Command+Option+Escape to bring it up.
Check the list for apps that are "not responding" and force them to quit.
Edit: orrr you could always do hard shut down 😀 (hold down power button til' the computer shuts off) and then turn it back on 😛
EDIT: You may have some serious problems if finder and software update failed like that. Try to reboot, if it persists, try repairing disk permissions in disk utility (found in Applications/Utilities folder)