Tom,
You don't necessarily need a firewall, as your Linksys router probably has a
hardware firewall built in.
Having said that, I do have a software firewall in addition to the firewall in
my DLink router. I do this because I don't trust the router to keep ports
closed when not in use.
AdAware is not a firewall program. AdAware is a program which scans for, and
hopefully, removes spyware which already exists on your computer. There are
also spyguard programs which function differently than AdAware in that their
function is to prevent you from getting spyware in the first place. In other
words, they are proactive.
HTH,
Steve, K8SP