I'm not sure you can log on from DOS. You need a DOS client, and I know
there's one for Windows 95 (it's on the Windows 2000 Server CD), but there
isn't one there for DOS.
Just create a network boot disk from the Win2k CDROM or find help from the
Internet. There are many Network Boot Disks available that use TCPIP to
access a Win2k Server.