Jules used a normal tripod folded up and bungeed to the rear bulkhead for his famous flip video, seems cheap, versatile and surprisingly stable (the tripod, not Jules )
I've tried a few homebrew and commercial mounts and unless you spend a decent amount of cash it's very hard to get something that works under vibration. Nigel H had a suction mount (a very expensive one I might add) that worked really well, he even stuck it to his bonnet at Slindon
Mini DV cams are cheap nowadays, I wouldn't go for anything too expensive as it will discourage you from using it in slightly risky situations (either that or make sure it's insured with a very understanding company ) some of the best shots are gotten by risking the gear. You can get firewire cards for PC's and laptops for less than £20.
I bought a USB video converter (analogue in, AVI/MPG/whatever out) but it takes a load of processor power and ends up dropping frames at higher (read: decent) resolutions. Firewire I think transfers the DV data stream direct so is less CPU intensive as long as your HD can keep up.