Active Directory & DNS Puzzle!

One of my clients networks has a DSL Router configured as DNS Server & as Default gateway.
There is also a single 2000 server running DNS & AD Services. The network uses private IP’s (10.x.x.x.) including the server. With the DSL router as DNS & GWthe Internet functions fine but logon from XP Prof. workstations is extremely slow (takes very long to find 2000 server). If I add the 2000 server IP to the list of DNS servers there is no longer internet access(tried 2000 server IP as primary & as secondary)but the logon is much quicker.
How can I configure the 2000 server and/or XP clients so I still have Internet access and keep the logon shorter?