We have a Snap Server 1100 on a workgroup at work and I spent hours trying to fix the "" appending in front of the username until I found this thread.
For others out there in the same position as me here is a quick step by step guide on how to modify Vista and fix the backslash problem.
1) Click Start
2) Click Control Panel (not classic view)
3) Click System & Maintenance
4) Click Administrative Tools
5) Double Click Local Security Policy
6) On the left pane, click to expand Local Policies
7) On the left pane, click on Security Options
8) Now, on the right pane, near the bottom, click on
Network Security LAN Manager Authentication Level
9) On the drop down, change the default setting (NTLMv2 only) to
Send LM & NTLM - use NTLMv2 session if negotiated.
Hope this saves others the hours that I wasted!