The file wininit.ini is performing the real update. When the running avast program is updated, its files are currently in use, so they cannot be replaced immediatelly. Instead, a number of .tmp files is created in the avast folder (those are the updated files) and the old files are replaced by these new ones on reboot.
So, if you delete the wininit.ini file, you avoid the actual update to happen.
In any case, this "replacement" should not take very long - the number of replaced files is not very big (20? 30?) - renaming 20 files should be rather quick. If it's not, I'd say your system have some big problem... a bad block in the system area of your harddisk or something like that. I don't think this problem is avast specific - if your systems freezes at this point ("Updating configuration files"), avast! is not yet active - so it cannot cause the problem, actually.
