I found this on the support forums for Antivir
This is the command you needed for antivir:
C:\Program Files\AntiVir PersonalEdition Classic\avscan.exe /GUIMODE=2
I've tested it out it works
The thread also said that GUIMODE=0 does the scanning invisibly
On a side note however: antivir has a higher virus detection rate than avast! or avg...antivir picked up a threat that avg had missed for months! worked its way into system restore too