This is probably a Windows 2000 issue.
Log to Win2000 as Administrator make sure that Guest account is not disabled.
Check the C: sharing make sure that permissions are all allowed.
Edit later.
If you are the only user you can, add the Guests Accounts to the Administrator Group, then log to the Guest account and put in an empty password that never expires.
Try to log again from the second computer if you get the password menu type the word Guest, and press Enter.