You can absolutely delete the .txt files. They're just text. You might want to open them and see if they're important first. (Wordpad, Notepad, ...)
The .~AV files... Never seen that before. When in doubt, you can always just rename 'em first then run for a couple of days to make sure everything's cool before deleting them. When I do this, I usually just append a .old on the end. Your computer will probably complain ("Are you *SURE* you want to do that??? Doing that might make the file unusable...) but go ahead.