Short answer.
Dont.
its not worth it. Ive tried with another bike. its just too noisy to hear properly and if its a 6 volt battery, you will have serious problems trying to.
Wear a personal stereo instead. HOWEVER.....
Longer answer.
if its a 12 volt battery you can get a car sterio from halfords or wherever (and a couple of speakers) and wire it up from the battery terminals. one bike stereo.
Make sure you install it in a waterproof container (like a backbox if you have one, or under the seat) screwing / glueing the stereo's cage down to the side to hold it in place and then you come into problems tring to change volume etc.
OR
If budget is not much of a problem then get a stereo with a remote stalk on it to mount on the bars and a waterproof enclosure (From the likes of maplins) to mount the stereo in the enclosure at the front of the bike at your left knee.
remember... seal every hole you make with silicone.
eab
February 2006