HERE dating back two years (many others after that time) - for uploading pics, the iPad recognizes a DCIM folder on a digital camera's SD card (now you might be able to 'trick' the device using an USB flash drive w/ a DCIM folder as described in the video) - the individual images must be labelled in a similar fashion to those taken by the camera - a search of the forum will likely bring up many more hits on this topic.
Bottom line - if you are only interested in getting images on your iPad using an USB flash drive, then you will been a CCK and will also have to put the image files onto the drive w/i the requirements in the first paragraph; it is easier to use a camera's SD card for these purposes. AGAIN, if you are trying to 'format' an USB flash drive to do other that transfer images, then NOT a possibility - see the other suggestions. Good luck and if you indeed find a way to transfer non-image files via a connection to the iPad's dock station, then please let us know! Dave