Network problem

In my network, I have a Win2000 Desktop and laptop and a new WinXP desktop. Here is what is rally bizarre!!!

The XP machine can access files on the Laptop,
the Laptop can access files on the XP machine,
the Win2K desktop can access files on both the XP and Laptop. But neither XP nor Laptop can access the shared files on the Win2k Desktop!!!!

I have checked the shares, permissions, and usernames and passwords. I even logged on to each computer with the same username (administrator rights) and still cannot get from laptop or XP to Win2k!!!!

The error message states something to the effect of “user does not have the required login type”

Any Ideas

I would prefer not to have to reinstall windows, but if I have to, I will.Thanks