Good suummary.
We were having the same problem at one site, except it had Win 2000 TS SP2 and WinNT SP6 on its file server.
Problems went away upon installation of SP3 on the Win2000 machine and no patchs were reapplied on it(not sure if we actually had them set entirely the way you are specifing here).
Cheers,
Tom
Life happens, don't blink.