Vista - Network Discovery Problem with Vista Ultimate

Hi,

I recently bought windows vista Ultimate 32bit and I've installed it on my
main machine. In my home I have a lan network which I use to distribute files
required for my work. After I installed windows the computers in my Network
folders where totaly gone and I couldn't find them at all! I've enabled the
Network Discovery and File Sharing but it didn't help. The funny thing is
that my computer is accessible by the other computers as long as I use my
Admin passwords to log in. That's pretty annoying, any1 can help before I
contact support?

Note: The other 3 pc's that are in my network the two of them run windows XP
Pro SP2 and the other one Windows Server 2003 R2. My router is Cisco 876w.
Everything was working fine before I upgraded.

Any suggestions?