Just like Eddy said you should upgrade to Avast 2014. It runs fine on XP (with SP3) systems. Old version of avast can be downloaded and installed from here http://www.oldapps.com/avast_antivirus.php
Thanks for the detailed info. I have one last question though: when you say that support of v.6 will be dropped does that mean that v.6 users will not be able to update their virus definitions?
Why am I asking this? Because if v.6 still can get new virus definitions then I will stay with it no matter what Eddy says (no disrespect meant), because this is the only thing I am interested in:
a) I understand the v.6 is old and may lack new non-critical features - I am not concerned since I use only 2 shields (just as an additional insurance) and mainly use my copy of AVAST for manual scanning of the files that I bring on this computer.
b) I understand the v.6 is old and may lack new critical features - for example the support of new packets, updated behavior analyzer, etc, etc. Well, it's nice thing to have them but nothing new (the software) is going to be installed on this particular computer, web browsing is done on a different computer, no IM, P2P etc was ever installed here and never be. The system itself was installed 7 years ago and still runs as it was done yesterday (over those years the size of system drive grew by 5% only). That is why I immediately refused (I hope it sounded very polite) to install the service pack, add some more memory, a new disk, reinstall/repair something etc after one of my applications, working for years, stopped working for after the last update. The common sense just tells me that it isn't a case. And when drake127 mentioned the version, it took me just a few minutes to figure out what actually happened (because I had kept the logs and the multiple snapshots of the install. directory).
AVAST is the only antivirus software I run on this computer, over the years of its use and observation I developed a certain level of trust towards in software.
So, at the moment I just need the AVAST's ability to scan a file on my request for known signatures using the latest vir. definitions and that's it. Therefore, if v.6 still will be able to work with the latest signatures then what is the point for me to upgrade if I am not going to use all that new (and no doubts very useful, in general) functionality?