Use Vista's own firewall,it has inbound and outbound protection capibility.
Avg free Antivirus click here
Add a few other programs such as:
Spybot Search and Destroy
All free and found at Filehippo.
Then add ccleaner click here or again found at Filehippo.
Ccleaner will tidy up the computers obsolete registry entries/temp files/cookies etc.
Using these weekly should be more than enough to secure your computers.
Obviously the best security,is common sense.