Syntax for telnet is "telnet ip port" separated by spaces on both OSs.

"Permission denied" is a (heh) permission denied error. Your username or password is wrong or the user you specified has no access rights for that resource (did you add the user to the share?). On Windows, correct user/pass but no permission still mounts but you can't access the mounted drive or folder.

And finally, the fact that the Windows machine responds to the request (failure is a perfectly good response) leads me to believe that ports are correctly forwarded and WM is working fine.

It's probably the server. Most likely, you need to login before accessing any resources, which is AFAIK not possible with N900 at this time.

Listings on Windows are done via NET VIEW.

net view \\192.168.2.110

I think the Debian equivalent is smbclient -L hostname. Don't think it's on the device though.