Hey there uforgot...
Like Mallio says, you should define what type of riding you are going to do on the road as there are different bikes for different purposes, and your training will also depend on what you want to do too.

However, I suggest you do get a road bike as they are much lighter and made for the road and you will go faster and more securely on a road bike than on a mountain bike or a hybrid bike.

Its like comparing a SUV or similar with a family car - one is made for all terrain, and one is made for roads... a SUV or other 4WD will not hug the corners as well, will not zip up hills as quickly and will feel heavy and clumsy using uneccessary fuel (ie, your energy) as it pulls its heavy self along.

I would suggest a middle entry road race bike... don't spend heaps on bells and whistles like carbon fibre bits etc. If you are interested in TT, you can pick up aero bars and attach them. Have a go at riding with others, try things out... then your entry level bike can become your training bike, and you can buy yourself something specific that has a few bells and whistles.

Good luck and I look forward to hearing about your progress!!!