OK - I will probably be corrected on this, but I don't think the iPad can play Flip video files without being first converted into a format appropriate for the iPad.
The iPad can accept..
1.H.264 video up to 720p, 30 frames per second, Main Profile level 3.1 with AAC-LC audio up to 160 Kbps, 48kHz, stereo audio in .m4v, .mp4, and .mov file formats;
2.MPEG-4 video, up to 2.5 Mbps, 640 by 480 pixels, 30 frames per second, Simple Profile with AAC-LC audio up to 160 Kbps, 48kHz, stereo audio in .m4v, .mp4, and .mov file formats
and I don't think the Flip stores video in these formats. As I mentioned, I will probably be corrected, but I think you either have to use a third-party app on the iPad that can accept the Flip video format or convert them on your PC first of all.
Tim