Dave,
Check and see if you already have a hole in your boom. My vang had never been installed and I had the same question until I looked at the boom and saw the holes were already there. The bottom of the vang connects to the baseplate of the mast, you can see a "lip" with a hole at the end. This is not mine but here is a good pic of the setup. If you need, I can measure the distance of the hole from the front of the boom for you. Timmay!!!
Click to enlarge...
We run a Boomkicker (in place of a topping lift) and a Boom Vang (similar to what is in the above photo), although I run the vang control line aft to the cockpit, parallel with the Centerboard line.
In the photo (above) the vang line is cleated on the end of the boom. I personally do not like this set up, because it does not give you access to trim the vang when under sail. As the vang is used primarily to control sail twist and boom rise when sailing downwind, you would need to sheet in the boom to trim. With the vang line led aft, you can trim with the sail full.