I have an 8100 that I was using as a mass storage device under Ubuntu 7.04. It had worked well, transferring files with little argument until, mounting and unmounting well. This morning, though, it would not unmount properly, and it had to come with me, so I pulled the plug on it. When I looked for files on the memory card, it didn't show up, and the Memory Card settings said that it was in use as a Mass Storage Device. I tried a hard reset, taking the battery out and such. Now it says that the card may not be formatted correctly. How do I fix this?

Boy, does not sound fun. First thing I would do is a get hold of a card reader, put the chip in that reader and plug that into your linux box and check it out; it's possible you've damaged the partition table or something on that SD card accidentally - maybe it was in the middle of writing data to it, yanking it out caused garbage to happen?