Well, I can only get my laptop to talk to the main PC with all the firewalls turned off, which makes me feel a little naked! I can't get the kids PC to talk to the network at all, although it appears in the workgroup. I tried all combinations of turning different firewall settings on and off, but have had limited success.
I heard a rumour that there was a patch launched only days after SP2, but I can't find it anywhere (see
this
I just wish Microsoft would warn us if their service packs are going to screw up our computers...