I'm not sure why the Haupauge WinTV card isn't working, but I can recommend the Rainbow Runner for G series, but Matrox. This little card has just about everything, including MJPEG hardware acclerated compression, a full set of composite/S-video input/outputs, and more stuffs. Easily the best consumer grade TV add-on for the G400/MAX. Which should be expected, since Matrox made it themselves.
If the RR is too expensive or you can't find 'em, I believe the ATi TV Wonder VE should work with the G400.
For you're Haupauge problems, go to
Matrox's Official Support Forums.