Check this out http://www.homebrewtalk.com/f11/improved-boiling-stovetop-53683/
If you have to stick with the glass stovetop this may be your answer.
I used to boil on my glasstop...and besides the LONG time to get 4g to boil (and that was the extreme max) I'd always get a boilover from boiling with the lid on
I used a 5g SS pot I got from Wallyworld that I still use for boiling sparge water on my propane burner...at least till I get me e-HLT/MLT built (POL design baby)
But have you considered using a heatstick to assist the stove top brewing?
I'll see if I can get that heatstick link...
Here it is: http://www.cedarcreeknetworks.com/heatstick.htm
I gave in and bought a turkey fryer thanks for all the infos.