Are you running any other programs at the same time? Do you have any OS "enhancements" installed?
Try disconnecting from the interenet by either unplugging ethernet or turning the airport off.
Try deleting fcp preferences
and here are some more troubleshooting tips
No anti-virus running....
I disconnected internet and killed all running programs with same result in FCP
Here's a little more detail....once FCP is launched I can choose any open window, Viewer, Canvas, Timeline, etc. Assuming I've got the "Viewer" window active...the first time I click on a draw down menu it doesn't react to my click for about 4-5 seconds. After that, as long as I keep that particular window active the menus react correctly and instantaneously. That is the same case for whichever window is active, but since you go from window to window while editing, every time I make a new window active the delay returns for just that first click.
My instinct tells me it's something you've got loaded on your system. Did you try all the troubleshooting steps? What kind of drives do you have connected, and how are they connected to your computer? Any drives that are not formatted macosextended? Try disconnecting all external drives and see if that makes a difference. Do you have a MINIMUM of 10% free space on all drives and at least 15 or 20% free on your startup drive? If you have diskwarrior, run it on all drives. Boot off your os install disk and run disk utiltity disk repair on all drives.