SP2 is the minimal requirement. It will work fine with SP3. It should also cause no problems with your antivirus. You can only use one firewall at once. I wouldn't be surprised if the installation of comodo automatically disables the windows firewall.
They have free trials, so why not just try it and see if you like it? If you don't like it, simply uninstall it and enable your windows firewall.
thank you so much for your important reply,You have also broken my wrong concept on comodo,I thought that comodo is a freeware,but I was wrong and now I am going to try the trial.