Hi, please exuse me im new, ok i run Windows XP Home, and Avast 4 Free Edition, and i want to use the Windows Scheduler to schedule a scan of my system every week, so if i forget, it will do it for me. Trouble is i dont know the exact scanner module of the program to be able to schedule the scan.
Well this question has been discussed many time here 
You can do a forum search and you will find the answer 
Whilst the link that Tech gave you is a work around, I don’t feel it is a good solution.
The major disadvantage with the task scheduler trick of using ashquick.exe is, it will scan every file of the hdd, partition, folder or file that you set it to scan; even those files not considered a potential threat, this can take a long time.
The Pro version gives a lot more flexibility and the scan would follow the settings and exclusions, etc. of the regular scan.
I prefer to do a manual scan with my regular weekly maintenance tasks.