Ahh, ok...i thought those were all different classes. What are the pros/cons over choosing one side over the other? is it just the abilities you gain access to? or is there more to it?

It comes down to the plot... why not just play and see for youself ;)
As for which class got which skills, you got a nice table in manual.

In some cases, it is the abilities (like in monk's example). Then are two magic schools, which are tied to their sides - light magic (more of buffing and anti-undead) and dark magic (brutal direct damage spells). They will be available for sorcerer/cleric at GM levels and paladin/archer at E levels. And your sorcerer can get promoted to lich (dark side), which will change his appearance to a lich.

As a bonus, with the light side you can exploit one glitch to get almost infinite money.

Thanks!

At a certain point in the game you will be asked to chose a judge. Make a save game at that point as it will determine if you're on the good or bad side.