If you run into a problem where a downloaded file cannot be verified, there are a couple of options you can try.
Fixing corrupted iMovie files
Corrupted Quicken Quotes file causes crash; fixed via ResEdit
Readers warn against method for getting corrupted drive to be "recognized"
Time change bug and Adobe CS applications: Photoshop preferences corrupted
A series of fixes for eliminating this error message.
OS X Odds & Ends: Password length limit; TextEdit files corrupted
OS X Odds & Ends: Formac tevion tip; Fix for corrupted SmartMedia card?; Now Contact bug?
OS X Odds & Ends: Adaptec SCSI cards; TravelStar; Internet Explorer and corrupted support files; PGP
Oh, those terrible people at Google. In the latest "Scroogled" ad, Redmond says Google is peddling vitamin supplements to kids. And that's not all.