If your Windows 2000 DHCP server performs dynamic updates for its' clients, the PTR records that are created in the reverse zone are NOT deleted when the lease expires or is released by the client. This buildup of PTR records can cause a reverse reverse lookup to yield strange results.
To work around this feature:
1. Open the DHCP snap-in on your server.
2. Right-click the server and press Properties.
3. On the DNS tab, select Discard forward (name-to-address) lookups when lease expires and press OK.
NOTE: You can perform this procedure on a scope instead of in the DHCP server properties, if not all scopes are configured for dynamic updates, or if you don't want to delete the PTR records for all scopes.