Basically it is a restriction of the Home version, these advanced automated options are only available in the Pro version. The programmers have to eat
In the Home version you can check the option "Don't show this window again" when the first virus warning appears, select the "No action" button. This way, no action will be taken and you will given the results at the end of the scan (and you can perform actions from there). You do however, have to wait for the first instance.
This should become less of a problem over time as avast should have cleaned your system and the resident scanners should catch infected files hopefully before they are saved to your HDD.
I suspect you are also doing a Thorough scan with Archives enabled ?
Archive (zip, etc.) files are by their nature are inert, you need to extract the files and then you have to run them to be a threat. Long before that happens avast's Standard Shield should have scanned them and before an executable is run that is scanned. Thorough is also by its design very thorough and perhaps a little overkill for routine use, were a Standard scan without archives should be adequate.
I have only ever done a through scan with archives once shortly after installation just to ensure a clean start state, but with XP for example avast will do a boot-time scan after installation if you select it, this I believe will be quicker and reasonably effective. Like everything in life things are a compromise.
