If DHCP is configured with the following in the DNS tab:

Enable DNS dynamic updates according to the settings below:
Always dynamically update DNS A and PTR records
Discard A and PTR records when lease is deleted

However, the XP workstation is configured with the default setting in the
DNS tab of the Advanced TCP/IP Settings
Register this connection's addresses in DNS

Which one registers the address in DNS? DHCP server or XP Client?

I'm having problems with duplicate forward lookup records and the reverse
zone not updating or deleting records properly...