This never used to be an issue at all, until shortly after Windows 7 launched, microsoft pushed a botched update to users, but we’ll get to that in a moment.
At some point, trying to get Boxee to connect to a Windows 7 network share promted for a username and password, no problem, right? Wrong, because it never worked, even if you entered your proper credentials in. For the longest time I had thought this was a Boxee issue, but boy was I wrong.
It turns out Microsoft pushed an update to “Windows Live Sign-In Assistant” that just BORKED some sources from connecting w/ the proper credentials. The easiest way around this issue is to just uninstall the “Windows Live Sign-In Assistant” That’s right, it’s that simple, just uninstall, and reboot both your HTPC w/ Boxee, and Windows 7 for good measure (Windows 7 reboot is required after the uninstall).
The next time you launch Boxee, go to the network settings and feed it your proper Samba credentials (Windows 7 box’s username and password that has access to the shared) and go from there, from then on out, it shouldn’t even be prompting you for a pass.