It's real easy to use and as an added bonus, it get's the damn things smaller than most if not all other progams I have ever tried
Download it here:-
http://www.zipworld.com.au/~gharris/adfopus.html
Start it up, click on Tool's then Batch Converter, self explantary from here
PS. God help you if WinUAE crashes BTW, you'll suddenly find a whole shitload of 880k files in your C:\ directory