If I were you and I had any realistic thought of wanting to actually try mountain biking, I'd get a mountain bike. As is mentioned above, if you really like cycling, you will buy another nicer bike not too much further along.
A road or hybrid bike will suck if you try to mountain bike with it. But riding roads and stuff is still fun on a mountain bike. Heck, back when I was young and poor I pedaled halfway across the country on a cheap mountain bike.
I also recommend a mountain bike because I think mountain biking is hella more fun than road riding. I've got a racy carbon fiber road bike. I haven't used it in two years. This is because even when I'm intending to go for a road ride, I take my Salsa Vaya so if I pass a trail head that looks inviting I can decide to take it. I'd always mountain bike and never road bike if time to trailhead weren't a factor.
Finally, someone above said get fingerless gloves. Gloves are good, but if you're going to mtb, get gloves with fingers.