The problem though with avast is the free version has no scheduler
Tony,
go into windows / all programs / accessories / system tools / task scheduler
or
control panel / system maintenance / admin tools / task scheduler
click on action / create basic task
give it a name ie avast scan
trigger will be daily or weekly etc, it will then ask you to set the time of the scan
next - action will be start a program
the next widow will ask you to browse for a program. You want to type this into the box or copy & paste
"C:\Program Files\Alwil Software\Avast4\ashQuick.exe"or browse for it under program files\alwil\avast4 then click on ashquick
the text box underneath will ask for arguments - here you need to type in your drive letter
C:
or whichever drives you want scanning - could be C: D: E:
Click finish and you will have a scan scheduled for the time you entered either daily or weekly.
I can recommend the following free security programs
Rising free av - 2009 has a firewall now
Threatfire
Avira personal
Sandboxie
Comodo firewall with defense +
Returnil VS
spyware blaster
All of the above are pretty easy to use for most people