Shoutbox

You say that you are on the same domain: do you mean that you are part of a Windows Domain network, where you have to login to a network?

If yes, the only place you can create an account is through Active Directory on one of the network's Domain Controllers.

If no, or you have no idea what I'm talking about, then you can do this through the Control Panel on the remote computer, and find User Accounts. You will need administrative privileges to do that.
If you want to add a user as a remote user, then this is done within the Control Panel as well, using the item called System. Go to the Remote tab, and choose Select Remote Users.