For training plans ideas, I suggest checking out Ed Pavelka's book on Long Distance Cycling:
http://www.amazon.com/gp/product/157...186433?ie=UTF8

You can certainly do a century on a hybrid, but it will be more of a workout: road bikes are lighter and made to have you sit in a more aerodynamic position, so it's less of an effort to ride them. You can feel the difference after five hours! (I also find them more comfortable but that could be debated. They certainly offer different positions for your hands etc.)

I don't see why you would not be able to ride a century (at least a metric one) in a few months if you are dedicated to the sport. Don't burn out, ride that century and stop riding, though. Take it easy and choose manageable goals. You will certainly want to change your tires to slicker ones, they will make it easier for you to fly on that bike. Maybe clipless pedals (pedals you "click" into... I know it's strange they're called clipless) would help too, I found they made me much stronger on my hybrid when I first started riding. SPD pedals are not very expensive (but keep in mind you must also get shoes) and it's relatively easy to get used to clipping in and out. They will make you much more efficient, especially on climbs (you're not only pushing the pedals but also pulling on them).

Good luck!!!