1. Turn off the machines.
2. Unplug your modem
3. Reset your router ( with a paper clip )
4. Reboot machines.
This may take a couple of times to complete.
(xp does this sometimes)
I personally had to reset everything about 6 times to link my 4
XP pro machines together...
Make sure when you installed your Os's you didn't set mulitple "domains"
Workgroup will work fine.