Logon impossible due to addition of computername\ to username

I have an external 160GB HD networked to my Acer laptop running 64 bit Vista Home Premium via a Patriot GearBox USB Network Attached Storage (NAS)Adapter which requires logging on to with a hard-coded "admin" username and a password. Up to a couple of days ago everything worked fine and I could access GBs of music files to play on a wireless SONOS setup by logging on with "admin" as the username and chosen password, but for some unknown reason Vista started tacking on the computername\ prefix to the "admin" username. This is not accepted by Gearbox. I've searched many forums regarding this issue (this computername\ tack-on is apparently common since Windows 2000). Get-arounds are suggested, such as lowering security via registry changes (did so without success), or using variations of <ip-address>\admin for the username (does not work in a Workgroup).
Does anybody know how to enter a logon username (in this case "admin") to a networked non-domain non-Windows device?