Avast is a good free antivirus. I use malwarebytes alongside avast and it works great.
I just use windows firewall for windows 7. It is better than the XP firewall cause it has both inbound and outbound rules where XP had an inbound only firewall. Some people will disagree with me I am sure but the 7 firewall works good. But I am not against a security suite, most probably have a better firewall. Also if you have a decent router it may have its own firewall.