ahh the dreaded "super shimmies"
Firstly the access to the steering box is a cover plate just below the fuel tank on the driver side. You will see a plate about 100 mm in diameter. Take all the covers off and you will see it.
But..............
unfortuneately there is a fair bit you "may" need to do. Once you have solved it your car will be amazing.
There are a lot of rubber bushes in a super front end and these need to be changed to urethene.
Another culprit is the universal from the steering shaft to the steering box.
The following articles from Super Beetles Only percifically deal with the problem
read them and ask me more questions.
Have had the shakes bad and now my cars are a dream to drive!
http://www.superbeetlesonly.com/suspension/shakes.html
and
http://www.superbeetlesonly.com/forum/index.php?showtopic=1298