The Windows 2000 Professional redirector does not support RAW SMB mode, it uses Large File (CAP_LARGE_FILE) support, which is just as fast. Not all operating systems implement Large File support. Windows NT 4.0 implements Large File Read, but NOT Large File Write.
To work around this issue, use Regedt32, on your Windows NT 4.0 Server, to navigate to:
On the Edit menu, Add Value name SizReqBuf, a REG_DWORD data type. Using the Decimal radix, set the data value to 65535.
Shutdown and restart your Windows NT 4.0 Server.
NOTE: Setting SizReqBuf to 64KB (65535) should yield write performance that is approximately the same as a read between the two computers. The penalty you pay is that the Server service will use more memory.
NOTE: If you don't have any Windows 2000 computers in your Windows NT 4.0 environment, see tip 0405 » Reduce network delay.