I have gotten YouTube videos to "work" on my 3400, but very, VERY rarely. Interestingly, they were YouTube linked movies and not actually on YouTube.com itself. Nine times out of ten, though (more like 9.9 times), they just don't load at all.These days for a 'proper internet experience' you need at least OSX to access flash and other plugins. iCab is good and the old Mozilla is ok but only for basic surfing. Youtube would not work on iCab or Mozilla when I last tried it even with the latest flash that I could find for OS9.
Try VLC?