It sounds like you have a

It sounds like you have a Yellow RCA Video Jack coming out of your helmet camera. They call that Composite Video.

http://en.wikipedia.org/wiki/Composite_video

Most people will record onto a small camcorder like a DCR-HC32 or a DCR-TRV22, or something similar (cheapest solution). These camcorders record onto DV Tape. You can pick up these camcorders for $150 (used) or less of Ebay. There are two types of video (aux) inputs for camcorders. One type is a special SONY 10 Pin plug (DCR-HC32), and a standard3.5mm Jack (DCR-TRV22 and other camcorder models). You will need a interface between your helmet camRCA Jack, the the camcorder input. If you buy a camera with the Sony 10 Pin Input, you’ll need something like this:

http://www.xtremerecall.com/Products/Accessories_Helmet_Cam_Cabling.htm#Adapters

If you buy a camcorder with a standard3.5mm input, you’ll need something like this (PVS-6CABLE-AV 3.5mm AV Cable):

http://www.sportzshot.com/cables.php#

Below are some helmet camera manufacturers that will have helmet cam cables to solve your problem.

If you want to spend more money ($400+), you can buy recording devices that record to a hard drive (Archos), or that records to an SD Card (video quality not as good as DV Tape or Hard Drive)..