Since Win2K you have been able to use an IP address or FQDN in a SMB mount.
Could be true, but I think (sorry for being vague as it's been a while) that at the Windows security level if the FQDN host name cannot be resolved from the IP address then the login won't be authorised to proceed. But he's going the other way (W7 to Mac) so depending on how the mac is configured that limitation *may* not be an issue.
Typical of these sorts of problems his issue I feel is that the Mac's Samba hasn't been configured to use a suitable security mode (files, ldap, ads, and some others I can't remember), and his W7 machine's requests aren't presenting the correct credentials for the security mode used on his Mac, that is, I bet his W7 machine is sticking the workgroup in front of the username.
Samba doco is all over the place literally, and hard for a novice to understand. As I said before it aint for the faint hearted.
Life could be made simpler by just running Filezilla (FTP with an explorer look and feel).