im goin to try the same as you do in my test enviroment...
at this moment tho i cannot reach the avast website itself to download the server package... (i use ADNM in my production enviroment)
when i can download i will see about it.... if there is someone else with an answer in the mean time, they are welcome to drop it like its hot... in here
EDIT:
i just downloaded the latest version from the avast website and i can tick the checkbox for sharepoint 2007 (and 2003)