Decreasing value list

[purvisa]

I am (primarily) a home user, so I hope that my question won't seen to simple.

I am still using 4.1 (I'm a student...), and I have a database that I want to have display a list (check boxes or pop-up) that eliminates an entry when that entry is selected. I want it to simultaneously enter the value that is being removed into another field.

I realize that this will require a script, but I can't seem to make anything work. Any suggestions?