Is my HTC Hero SD card currupt?

I have an HTC Hero with the latest android operating system. Recently I noticed a quirk where the phone would not always register as a drive when connected to the computer. Now every few days about a dozen or more pictures/movies will become corrupt just displaying a "!" where they used to be, and then deleted by the phone a day or two later. This is a huge inconvenience as my pictures are important. Any ideas what this could be, and will I need to reformat my SD card?