Can't get Anonymous login to work with Windows XP

[chuffchuff]

I have Freenas 8 and followed the instructions for anonymous access. I set up guest with no password on Freenas, but when I try and access from Windows XP, i get a browser box which asks my username - I put in "guest" and the XP machone name is prepended to the username eg LAPTOP/guest so this doesn't match what I have set up in Freenas.