Do not allow users to decrement the number in a field

I have a document library.

The client have a field where they can enter their own version number. (i.e. 1.0.0.1)

Now if the original value is 1.0.0.5, and they edited the property and changed it to 1.0.0.1, the system should not allow this because the entered value is lesser than the original value which is 1.0.0.5.

Is there a way to address this?

Thanks!

----------------------- Sharepoint Newbie