Here's a picture of the new Kuryakyn Iso-Grips, after installation. Below is the basic procedure to fit these Harley grips on the Vulcan bars. There grips are very sweet on long runs, and have relieved my hand fatigue considerably.
I gleaned much of this from the VROC email archives, Tim "the Edge" Egger ~V~892, Tarkus, and others on the VROC Newsgroup.
1. Remove the chrome plastic end caps from the stock grips. They are reverse-threaded (left hand threads) onto the ends of the grips, so twist clockwise to remove them. They are secured with a little Loctite, so they're tight!
2. Some use a utility knife to cut away the rubber handgrips, then remove the grip top chrome rings from the handlebar (these may be held in place with o-rings). I found that I could remove the left grip by slipping a long allen wrench between the grip rubber and the bar, then twist the allen wrench while pulling on the grip. The allen wrench would "run around" the handlebar, and the grip would slide right off. You have 2 options on the throttle grip. You can separate the control head and remove the grip/throttle tube assembly (if you want to use the Harley throttle tube that comes with many aftermarket grips), or you can just cut the grip off as mentioned above and install your new grip on the stock Vulcan throttle tube. I opted to replace the throttle tube, since it was already the right length for the grips...
3. On the left handlebar, there is a metal threaded portion that is spot welded to the end of the handlebars for the stock chrome cap to screw on to. You'll need to remove this. Some use a hacksaw to cut it off, I used my dremel tool to simply cut the tack welds and snatch the little threaded insert out.
On the throttle (right) grip, the threads are part of the molded plastic throttle grip. If you use the stock Vulcan throttle tube, you'll need to cut them off, as they'll cause problems if you leave them on. .
4. The stock Vulcan throttle tube (white plastic) is connected into the throttle housing, and can be removed by unscrewing the two halves of the housing, and disconnecting the two throttle cables (one is for acceleration, the other is deceleration). The tube will slide right off the handlebar.
5. VERY IMPORTANT: measure the length of the new grips and compare to the length of the white plastic throttle tube. Chances are, the grips will be shorter than the tube. Cut off enough of the end of the tube to let it fit all the way into the grip. The tube should be at least 1/4 inch shorter than the grip so you don't "bottom out" when you try to shove the tube into the grip.
6. IMPORTANT: once you have satisfied yourself that the length of the throttle tube is proper for insertion into the new grip, check the diameter of the tube against the inside diameter of the new grip.
7. To avoid some of these difficulties, check before installation. In a set of two new grips, one may have a larger inside diameter than the other. If so, the bigger one goes on the throttle. On Harley stuff, the packaged grips may also contain a replacement throttle tube (black plastic). Unfortunately, the Harley tube is slight different than the Kawasaki tube, and won't fit into the throttle housing. You can correct the O.D. of the section that fits into the control head with a hacksaw blade or dremel tool. Be sure the throttle tube twists freely in the control head when you finish.