nah, no need for a reformat (at least not from the problems you describe)
The slow network bowsing can be fixed with the reg patch at my site
Click Me
We can start from the beginning:
Do you have all of the computers in the same workgrounp?
(Right click My Computer, Properties, Computer name tab)
Does each pc have a unique name in the same place?
(I E Pc1 PC2, or Office, Main, Basement, etc.,)
How are IPs configured?
(If you didn't do anything, the router is assigning them via DHCP, that is fine.)
Can you ping the other computers?
(Start, Run
ping 192.168.1.100) need the IPs of your networked computers.
Can you access shares with UNC path?
(Start, run
\\networkedPCname
Post what the command,
arp -a from the command line displays.
(This should show every computer in your network.)