Disable the built-in XP firewall - It's the cause of most of the software incompatabilities listed on the microsoft web site. I'm using Symantec Anti-virus, Zone Alarm free personal firewall and a hardware firewall using NAT (network address translation - makes a hacker's job a lot harder when attacking your system). I've never had any problem with XP, SP2 & Poser 5 because of this combination - I was using Zone Alarm before I upgraded to SP2 - I think that helped as well.