You could probably set up a pair of script triggers such as OnObjectEnter to perform a script to enter the current user or account name into a field in that record when a user starts to edit a field and the OnCommitRecord can run a script to clear the field.
This then gives you a field you can see from another computer to tell who has it open for editing.
OK that sounds like it will work, will try it. Thanks very much! It's much better than what I WAS doing (which didn't work).
Funny I feel like a pioneer asking this. Could a custom function do this?
I can't think of a way to do this with a custom function.
Thanks very much for that answer Phil.