protecting a single cell

Set the protection properties for all the cells to "Unlocked" and then set your one cell to "Lock". To select the entire worksheet, click on the grey box to the left of the letter A in the columns and above the number 1 in the rows.

Hope this makes sense to you.
Barrie

Okay, I hate to look stupid, but I don't get it. I tried the unlock/lock
and the message I got is that the worksheet has
to be protected first. I protect it and it won't
let me unlock/lock. What's going on?

thanks again!

I believe you will find the message says the locking will not take affect until you protect the sheet. So, when the sheet is unprotected, set the cell(s) lock/unlock property, then protect the sheet.