I have 4 home computers protected by PC Tools - both XP and Vista (however, it won't run on Vista x64). My kids and my husband prefer PC Tools, because they do not understand what Comodo says to them, and PCTools has Polish language verion. I installed both FW and AV (on my husband's laptop there is Spyware Doctor with AV module) and I'm really satisfied - no problems except the pendrive infaction of my older daughter, but PC Tools managed to block it. No stability issues, no problem with CPU or RAM usage.
Thats good. PC Tools is a great company, its just that their weakest product is their firewall, which isn't a big deal because a router is more then you need as far as a firewall is concerned.