Changing the starting number of the autonumber

[chiefbunny]

I have a table with a compound key, and one of the two fields in the compound key has to start at 100 and finish at 999 and I'd like it so that each number didn't have to be typed in individually.

So I thought about using an autonumber that somehow starts at 100 but doesn't go over 999 if thats possible? Or if you have any other ideas on how I could achieve this?
Thanks