I tried selecting boot time scan with XP64 and found it grayed out in Avast home. This feature has always made me come back to Avast time and again but now I am surprised it has been removed for XP64. 
Well, “removed”… let’s say the feature hasn’t been ported to support 64bit OSes yet.
Thanks Igor,
Hopefully it should be ported soon as its the only one that can scan, fix or delete stubborn locked files that have been infected.