I have installed Avast 5 on two PC`s with problems.
Installed on Vista laptop. Ran program to get warning box about a "side by side configeration" problem preventing it from starting.
Nothing about this in Avast FAQ.
Finally found answer on Google that Vista requires SP2 for it to run.
Why no mention of this on the web site ??
Second PC, found multitude of errors, however it would only clear 20 of them without demanding I upgrade.
Ok, had enough and reinstalled the trusty ver4.8