Well, .418 did the same thing in the same place. This is an older computer running at a little over 600MHz, so I checked the box that says "load Avast! services after system services load." This is a good optimization for older machines, as it lessens the startup load, and I very much appreciate its inclusion. I understand why it's NOT checked by default, but rather wish it were. But I digress.
Here's the behavior: system loads and working desktop appears. System works fine for some seconds. Orange A-ball appears with red X. Red X changes to yellow exclamation mark. Some seconds later, BSOD. This is repeatable. It happens every time. I even took out a memory stick to see if that might be the matter. This machine is odd about its memory, and will give a BSOD if you run 3 256MB sticks in it (known gremlin with that board) but I had zero problems with it running on 2 sticks until I installed A5.
I am attempting to upload my memory dump now, but my internet connection is somewhat slow and very cantankerous, so it may take a bit of doing, and I may ultimately do it from a friend's house. The file name will be kerneldump-edifyguy-xpsp3-avast5-0-418.7z or some variation upon it (depending on what happens with failed writes.....seems your server won't allow overwrites.)