it's pretty easy. pop over to terminal, and type in "sudo rm " without the quotes. then find that stubborn file on your desktop, drag it into the terminal window, and push return. It will ask for your password, type it in and then it will work. (you usually have to click on the desktop before it will update the display though)
If it's a folder we are talking about, I believe the command is "sudo rm -r " and do the same as above.
By the way,
Things like these are why OS X needs to mature more (i.e. APPLE, MAKING NON-OS 9 BOOTING MACS IS WAAAAAYYY TOO SOON!!!). What would the average Mom do in this case? Probably blame Apple which she is right to do because she doesn't know about macosx.com...unfortunately permissions on X easily get messed up, too easily if you ask me. Heck, if you install software as an admin, a lot of the time it doesn't work as guest! (try MS Office, TextEdit, etc. in Guest acct. - MS Office can't open a framework, TextEdit can't access the Spelling Engine and errors out after every word you type.)
