When a Windows 2000 DNS client sends a request, the entry is serviced by the client-side cache, until the TTL has expired.
This can give the impression that 'round robin' isn't occuring.
To view the client-side DNS cache, type: ipconfig /displaydns
To flush the cache, type: ipconfig /flushdns
While you can't disable the cache, you can set TTL to 1:
Edit or Add Value name MaxCacheEntryTtlLimit, a type REG_DWORD, and set the data value to 1.