I installed the new version on my WinXP svcpack 3 computer and it is using 99% of my memory constantly.
Should I try reinstalling?

I tried to repair installation and still had same problem.
In Avast ‘Statistics’ it shows the following files being repeatedly scanned:
http://192.168.2.1:36477/ctl/cmnIFcfg
http://192.168.2.1:36477/ctl/cmnIFcfg
http://192.168.2.1:36477/ctl/cmnIFcfg
http://192.168.2.1:36477/ctl/cmnIFcfg
http://192.168.2.1:36477/ctl/IPconn

I unistalled avast, rebooted, ran malwarebytes, ran ccleaner to fix registry issues, downloaded AvastFree from link provided in this original post. Seems to be fixed and back to normal.