Being that I just purchased and hv20 today, and I’m totally new to any variant of hi-def, I too was having trouble getting FCP to capture. I tried iMovie, and capture worked fine. So, I went back to FCP and checked out my Audio/Video settings, and discovered they were off. It was trying to do DVCPROHD60. I set sequence preset to HDV-1080i60, capture preset to HDV, and device control preset to HDV firewire basic. I tried to capture again, and was greeted with a different looking Log and Capture interface; similar to the one I see when capturing dv, but different. Everything then captured beautifully, and I was able to lay it on the timeline with no rendering required.
Hope this helps-
dave