I just recently replaced the top on my '98 Boxster, after it's plastic rear window had been destroyed by a hailstorm. I went through the back and forth about shelling out the extra money for a glass top, or saving a few bucks and sticking with the plastic window.
Ultimately, I stuck with the plastic window, but if you want to save yourself a small fortune over buying direct from GAHH, go to this website instead:
http://www.autotopsdirect.com/Boxster-Glass-Windows-s/97.htm
This company sells the same exact product, made in the same exact building as GAHH, but for considerably less money. The UPS info said it was drop shipped from GAHH's address, and the fit and finish on the top was just like OEM.
Price is either $529 if you choose the Twillfast material, or $599 if you choose the German A5 canvas (which is what I chose for my top with the plastic window. That will save you around $325, right off the bat, but you don't sacrifice on quality, one iota.
I installed mine myself, with the help of a friend during the assembly procedures.
It was both challenging, and yet, quite straight forward.
BC.