comodo V3 firewall not conflict to avast! at least i don't find any problem
I had been used them from V3 issued to last week.
But i had uninstall comodo v3 firewall at last week because i believe avast! is wonderful with xp systemic firewall .Another reason is comodo v3 firewall affect my net speed ,although somebody don't think so.
If you had a good manner in internet ,avast! and xp oneself firewall suit to home consumer.
Of course , i will recommend comodo v3 firewall if you want a firewall except systemic firewall,because it's Advanced+ is great.