Reset userid number when re-running import

I'm importing data from phpBB 2.0.22 using ImpEx 1.96. We have ~2,000 users in the old forum. When I ran it the first time, I got new userid numbers in the 1 - 2,000 range. When I deleted the import to re-run it again (using the 'Delete Session and all imported data' link), it deletes everything, but the next import I run I end up with user numbers in the 2,000 - 4,000 range. The "next user number" counter never seems to get reset.

Is this on purpose? Is there any way to reset that back to 2 ("admin" is the only user in the new database; all the rest are imported from the old forum)?

Or is this something I should be ignoring and not worry about? :)

Thanks!
Rich