This question comes up almost daily!
Before you install any other software, you'll need to remove Norton. You can't do this from 'Add/Remove' programs. You have to download the removal tool from here:
http://service1.symantec.com/SUPPORT/tsgeninfo .nsf/docid/2005033108162039
The vast majority of the 'regulars', in AB's Technology section (myself included) use Zone Alarm Free Edition as their firewall. (NB: Use the bottom link. The upper one is for a time-limited trial product):
http://www.zonealarm.com/store/content/company /products/znalm/freeDownload.jsp
and AVG 7.5 Free as their anti-virus solution. (Use the right-hand link):
http://free.grisoft.com/freeweb.php/doc/2/
Those programs are usually 'topped up' with anti-spyware programs such as Ad-Aware SE Personal
http://www.lavasoftusa.com/products/ad-aware_s e_personal.php
and/or SpyBot Search & Destroy:
http://www.safer-networking.org/en/download/
Chris