firewire is the way. the helmet cam plugs right into the dv camera. i use a sony mini dv camera (shoots in 480p) and the helmet cam is basically a viosport but under a dif name. it uses the sony ex lens/ccd. the minidv is no more or less subject to shaking than the hdd camera. the hdd camera is usually cheaper, but limited by several aspects including storage space and record speed.
my helmet cam has it's own power supply, something like 8 AA batteries. it's heavy when combined with the camera and all the other crap in my camelbak. however, this gives it excellent shooting time. the hdd ones sometimes are integrated and use a common power supply that doesn't last as long. so you wind up taking along just as many batteries and changing them often. 6 of one, half dozen of the other, it's really the same thing. i looked around alot before i bought mine and decided i wanted the versatility of having the mini dv for normal use and being able to add the helmet cam to the mix whenever adventure called (or bombin4x has some crazy downhill he wants to do so he can see his dh bike bouncing along the trail like a pogo stick!)
the things you'll want to remember is not to turn your head to look to the sides of the trail, don't look down at your feet/chain rings much, these are the things that make the viewer get all seasick... having the minidv camera does make it easy to unplug the helmet cam and hand it off to someone for off-bike shots. also, remember to wrap the all the wires together and run them through either the shoulder strap of your camelbak or your shirt sleeve. this makes it less likely to snag on something (branch, bar ends, etc) as you film.
bring extra batteries and tapes. you can film the whole day that way where using the hdd type of camera usually requires downloading the images to free up memory for more filming. some of the hdd ones have a limited memory and unless you want to bring your laptop along to download at the car halfway through the day, it's easier to change tapes. they also make cameras that use flash memory and this works well, but for the price, tapes are cheaper. also, the hdd type might give some 'pixelation' of the image at speed whereas the mini dv won't show this defect as much. it's really about the speed of the recorder/camera and the tapes usually record at a higher speed. and yes, you can use a different lens with the mini dv camera. i have several including a 'fish eye' and a macro that zooms in a ton.
don't forget to check the lens after each run for dirt, dust. and don't forget to make sure before you start the camera is oriented in the mount the correct direction (personal experience!) otherwise, it's all pretty simple really and easy to take the camera when done, plug it into the pc and download it. then you can edit, burn to dvd, and amaze (or sicken) your friends. i use adobe premiere and a combination of dvd editing software. the software that sony provided with the camera sucked. any more questions...feel free to ask. i'm currently working on building a watertight plastic box for my camera so i can take it snowboarding. but it's been great for biking.
hope this helps...
p*
