How to install Comodo?

I know how to do normally, but I had Comodo Firewall installed once before,uninstalled it so I could try some other brand. Currently have Outpost, but want Comodo back instead. Will not re-install, even when no other firewall is present. Message box says "You see to be trying to install using an older installer ". Went through all program files and can find no mention of Comodo, but when scanning with anti-spyware, see Comodo name flash up.Start,run,search for Comodo shows no results.Any ideas,people.