This isn't an issue in avast7 beta on my system XP Pro SP3, see image, nothing crucial, like the buttons being clipped in avast6 example. As for the left side, that is just the Orange 3d effect, so I don't know how that might be reflected in the windows full screen, but nothing crucial is effected.
I honestly can't see the point in using full screen, especially when I have a 1920x1200 26" TFT monitor. Even on my win7 netbook, 1024x600, the last thing I want to do is go full screen, I'm permanently trying to reduce the sizes to a minimum...
EDIT: Typo.