Excel Macro

Hello everybody,
Need a quick question answer. I have a macro in Excel 2000 that will find the first empty cell in a range, fine. This should happend when the “cursor” moves to a specific range (cell). I have already tried to do a “hot spot” but unless you “click” on it the macro will not run. I need it to execute as soon as the cursor gets to the specific cell (either by tab or arrows).
Thannks,
Henry