Yeah, the openGL patch was developed about 7-8 yrs ago - very hard to find. Since the source code for Doom was released to the public a few years ago, I think you'll find there will be a lot of patches for Doom/Doom II, that will have openGL as well - the one you mentioned zdoomGL does have it I think.
Another good program is called mame (just google for 'mame'). You can download 'Rom's' which is the data downloaded from the old arcade games machines memory chips - e.g. Battlezone, Galaxian, etc.
You can play the old arcadies(yes the actual same one) on your PC, doesn't need a high power PC either.
Now they bring back memories . . . .

Cheers man, you're a legend

i love that game transport tycoon...lol...i still play it, check out openttd.org for a new kick a** version.

for your games try abandonware sites such as, http://www.the-underdogs.org/

hope it helps.