I use a dynamic dns service, no-ip, which automatically points towards whatever my external ip happens to be.

I need to be able to resolve an internal ip address for the name used by the dynamic service, without stoping resolution to other external no-ip addresses, i.e. for use with smartphones which connect via wifi when in the building.

Any pointers on how to do this with the standard dns server iin 2003 would be appreciated.

I'm not 100% certain I understand what you're asking, but let's say your no-ip address is joe.no-ip.com.  Create a new primary zone named joe.no-ip.com, then in that new zone create a new host (A record) and put in your internal address.  Then your boxes which use internal dns servers to resolve would come up with your internal address, and those out in the real world using someone else's dns servers would get the external address.

 Is that what you had in mind?

That's perfect - just what I needed.

 Thanks.