Erm, last time I downloaded and burned under windows, I d/l'd the iso's, then the md5sum file (not the one called ascii or whatever, just md5.
You should be able to print off the md5, and it "Should" give you either an md5 for each iso (that's if there's an md5 file for each iso or if it's just the one md5 sum file, it should have all 3 md5 numbers for all three iso's).
Not sure why you'd use pgp or whatever.
Then you open the md5summer app, and you want to "create sums" - i.e. dig through until you've got the iso that you want to check, highlight it and then hit the create sums button.
You should (in theory) then have the md5 sum for the iso that you're checking and it should match the number in the md5sum file that you d/l'd from the mirror.
If it don't, then re-download, if it does, then you can burn the iso image and you should be ready to install.
Should the number not match, you could still burn the iso, but it'd probably have corrupted sections/files and if it's something that you can't get through updating etc then that wouldn't be of any use!