winxp-sp2 does not recognise domain

I have Win XP Pro SP2 fully updated on a large network and the domain controller is WIN2K SP4 Server with DHCP enabled. My PC connects to the domain smoothly without any errors. But problem starts when i assign a static ip along with the DHCP address. Like when i connect to DHCP i take the automatically assigned IP address and manually enter it in the TCP/IP config box in network settings, and then also enter my static workgroup IP so that i can access both domain and workgroup. This scene works absolutely perfect in Win2K Pro, but doesn't work in WinXP SP2 Pro becoz it doesnt recognise the logon to the Domain. I have tried adding domain administrator account in the Control Panel USERS but still it doesnt work.