Vista - User name definition in ad hoc connection attempt

I have sharing set up, on an ad hoc network. Everything except logon is
successfully connected. In Windows Explorer, I click on 'network' and get
shown 'JoesHP', I click on that then I get a sign-in box with User name, and
password required. What is the construction of the User name? Is it just the
user account name at the destination JoesHP? When I've tried just the
destination user name eg Joe (the admin account on the JoesHP machine), and
the password for that account on the destination machine, I get refused
access with a message "Logon unsuccessful" What user name are they looking
for, the login end (here)? or that I'm trying to log into there?, what would
be an archetypal username construction, eg JoesHP\Joe or just Joe, and, which
password are they requesting- *here*? or *there* at destination trying to be
logged on to?