I've done this before with decent results, but I would like better quality. There are really 2 ways to do this. Wired or wireless. If you go wireless, you carry less gear, a camera/transmitter and battery, but the quality isnt nearly as good. Especially if you are playing in a wooded area, the range will suck. Plus the transmitter and receiver will make the whole thing more expensive. Really not a good way to go, especially if you want quality.
I would highly recommend wired. Which is what I am going to do as well. The archos that dman suggested is a very good idea. Dont go cheaper than that. I bought a cheap PVR on ebay for $50, it worked, but it wasnt too great. The archos isnt very big either. It can easily fit in a vest pouch. The only other thing you need is a battery and camera. As suggestions, you can look at one of these:
http://www.bulletcam.com/helmet_Cams_products.htm
http://www.hoyttech.com/index.cfm?fu...Product_ID=295
An archos will set you back a little over $500, and a camera about $200-$350 depending how good you want to go. So in total you could get a very respectable cam setup for about $800.