You can disable resident protection from simple user interface using its button (its look depends on used skin but generally this button is labeled with "a").
In enhanced user interface simply right click over resident task with check mark ("Resident protection" task by default) and choose "Unmark" from popup menu.
Another solution is to stop service of avast! (it works only in Windows NT,2k,XP) within "Services" administrative tool. But I cannot recommend this method because you will disable other parts of avast! too (virus chest for example).