DNS weirdness

Single domain. Internal DNS, External DNS for DMZ machines.

About every hour, win2k pro machines lose name resolution ability. An nslookup w/ set debug on shows an A record with the correct IP and Name.

An ipconfig /flushdns or ipconfig /renew will get the name resolution working again, but I cant really do that every hour for every machine.

What i dont understand is why it stops working, then will start working either after a renew, or a short wait (10 min).

K.