Choice between old and new API

I am doing research in computer graphics and have been using the
old HOpenGL to try ideas.
Recently I've wanted to use 2D convolution and discovered it wasn't
supported in HOpenGL 1.5.
I am a bit constrained by time (I have a Ph.D. to finish) and I wanted to
know what would be the easiest between:
-learning how to build the old HOpenGL 1.5 API and then adding the
 bindings for the convolution functionnalities
-or porting my existing code (which is around a few thousand lines) to
 use the new most recent API, provided it supports texturing and
 convolution

Unfortunately I am developping under windows XP, using the cygwin
environment. If I have to compile the latest version of the GHC
distribution to get those functionnalities, I am worried that it may prove
very time consuming. Assuming that this is not a problem, how different
is the new API from the old one ? Will the changes I'll have to make to my
old code be merely cosmetic or more in depth ?

Thank you for your help.

	Yann Morvan