It's in the Application shortcuts, since it applies to the Source Monitor, Program Monitor, and Timeline Panel. I don't believe it's assigned by default; it's simply called "Play In to Out."
If you're on CS5.5, just search for it in the Keyboard Shortcuts dialog.
Thank you Colin,
I feel so stupid, it was sitting right there in front of me. duh. I was digging through the windows sub menus.
Thanks alot Colin, I appreciate it.
a monday morning knucklehead
Hehe--no problem I can sympathize
The laughing Smilie looks just like you Colin ;-)