IPC$ error on connecting

hi,
1. I have MS NT domain & on double clicking on Network Neighbourhod see lots of systems on my LAN, now when I double click any of them , I get error msg ” Unable to login \\MI2\IPC$” & asks for a password. Why ??
2. how do I connect a Unix system on my Lan to access NT domain & access internet thru my NT Proxy Server ??
Akash akashdeep_b@yahoo.com