I downloaded Avast AV once Norton starting demanding money. I´ve just got around to uninstalling Norton (yes, I´m sure this was the wrong order).
I was reluctant to get rid of the whole Norton package as I thought there might be elements which the Avast package wouldn´t substitute e.g. the firewall.
During the ´uninstallation´ process I got the option to return to a default Windows firewall (does that make sense?) which I accepted.
So I think I now have Avast AV + a firewall of some class - is that generally enough or have I overlooked something?
If you are only using the XP firewal you should get a third party firewall to provide outbound protection, there are a number of freeware firewalls.
Whilst the windows XP firewall is usually good at keeping your ports stealthed (hidden) it provides no outbound protection and you should consider a third party firewall.
Any malware that manages to get past your defences will have free reign to connect to the internet to either download more of the same, pass your personal data (sensitive or otherwise, user names, passwords, keylogger retrieved data, etc.) or open a backdoor to your computer, so outbound protection is essential.
Zone Alarm free http://www.zonelabs.com works fine with avast and has a reasonably friendly user interface, however, the free version is becoming bloated with trial ware. There are others, Comodo, PCTools Firewall Plus, Jetico, etc.
You might also consider using Sysgate personal firewall, should you purchase a Seagate external hard drive (for backup purposes, say.) They’re relatively cheap, have good to excellent reviews, and come with software for the Sysgate firewall, which I find superb!! Just a suggestion. (No, I have no stock nor other involvement with Seagate.)