Originally Posted by senseamp
Does anybody know how th steerer tube is attached to the fork crown? Is it just pressed in?
It depends on the fork. My RST suspension fork uses bolts to hold the steerer tube in the crown. I purchased a 2nd 20" fork to modify, and found that it was all one piece. If you are in the USA, you can get the RST fork, which has an adequately long steerer for twenties, from either Gaerlan.com or Harris Cyclery's website. Harris Cyclery is also willing to thread it for you, if that's what you want.
As far as lengthening the cockpit and getting the handlebars up higher, I believe Jur's solution of using an upside down seatpost clamped onto the original fork and headset is the simplest. Of course this means you would have to use the original headset.
I myself added a steerer extender and used a "tarik device" pvc spacer with an ahead headset. My brother happens to be a machinist, so when he has some spare time he has promised me he would fabricate an aluminum steerer extender that I could clamp right onto the top of my fork's steerer. This would allow me to ditch the PVC spacer for a much cleaner look, while giving my steerer more length,
BTW, I'm 6' and I have plenty of cockpit space on my twenty. In fact the handlebar height would be just fine if it wasn't for my really bad back,