I used to install windshields, for 5 years actually. Most glass shops will not gaurantee removing the old one (I never did).
If you are getting a new seal, you can cut the old one out with an Olfa knife. I don't really remember how the samurai windshields were put in, but most windshields held in by a rubber seal are easy to install (IF YOU KNOW WHAT YOU ARE DOING).
DO NOT BLAME ME IF YOU BREAK YOUR WINDSHIELD!!!! DO NOT ATTEMPT UNLESS YOU ARE PREPARED TO BUY ANOTHER WINSHIELD. THIS IS PROBABLY ONE OF THE CHEAPEST WINDSHIELDS TO HAVE INSTALLED, YOU ARE PROBABLY BETTER OFF PAYING SOMEONE.
Basically, you clean the window, put the gasket on, and run a 3/16 rope into the pinchweld groove in the gasket. You then have one person hold the windshield against the car pinchweld, and a second person pulls the rope out, always towards the center. This will pull the lip around the pinchweld. As it nears completion, it should pop in. You might need a hook tool to help the bits that pop back out. Gently smacking the glass with and open palm will help it into position.
From what I remember, the samurai w/s was designed in a manner that does not easily allow back sealing between window and gasket, or between body and gasket. This means, if it leaks now, you should replace the gasket, you probably can't add sealant in a non-visible manner.
Good luck, MArc