May I ask what free version of the Avast program can be run on an XP machine that is a mere antivirus program and not a combined internet security suite with all the firewalls etc
All I want is a free antivirus program that does not combine all the firewalls etc ( keep it simple !!)
Thanks
Avast Free Antivirus would be your option.
You can choose custom install and untick everything that you dont need.
I am already using a custom installation of Avast free ( Avast 4 Home at present ) but which more up to date version of it is most appropriate for an XP machine ? I do not wish to mess up my machine by taking on a version not approprioate for my needs 
(I also appreciate that XP will stop receiving Microsoft Support in 2014 )
Its time to switch the computer soon.
But if you want to stay at XP you can use the newest version of Avast. (2014.9.0.2008)
Download: http://forum.avast.com/index.php?topic=139606.0
A program update will go out soon.
What for an hardware do you have?