lets see if I’m reading this correctly…
Firefly on server runs fine and 3 other computers (presumably something other than Vista) can happily connect to it.
4th PC running Vista can’t connect unless you log in as an administrator.
If I got that correct then it sound like you have to check the network access privileges for the general user account on the Vista box.
I’m not familiar with Vista so i can’t help you with specifics.
XP has a “Power User” access level. Does Vista also have this & can you access Firefly as a power user?