Haha getting a lock for the office is probably a better hint than locking your machine since unsupervised little ones (not to mention adults) can do much worse with expensive equipment than just renaming files!

Anyway I wanted to mention that I have tried to restore files that were in use before (ie. my entire /etc/ directory) and I just restored the folder under a new name and then connected the computer in firewire target mode to my MacBook (although you probably could just boot off of the OS CD or maybe into single-user mode or something) and then deleted the destination folder and renamed the one I had restored from TM. (In the case here I would go into TM on my iMac and restore the whole "Applications" folder to something like "Apps2" and then restart in FW target mode, open my iMac drive from my MacBook and delete the "Applications" then rename "Apps2" to "Applications".)