I started using Avast when the 4.7 version was around. I wonder how the older versions looked like (and worked). Is there a thing like Avast museum, where we can see the older versions, maybe some screen shots or a video? I’m really curious how versions 1, 2 and 3 looked like. 
Here is 4.5 to 4.8 but no screenshots http://filehippo.com/download_avast_antivirus/history/
I haven’t use version 3 as I’ve started with 4.0 some months after its release.
Version 4 was skinable since from the beginning. The number of skins grew up after some time (specially due to Sasha’s work).
All available skin are in the download section.
Wow, some skins are really beautiful! I especially like “Iconic” and “Flat’n’Simple”, but I’ll stick with the default one, because I’m used to it.