Agreed, work out a lot.
Ride up hills until your muscles hurt, then stop and walk it up the rest of the way. And rest for a bit.
You could also take it in to an bike shop, buy a thing of lubricant, and either have them apply it, or apply it yourself (they might tell you which parts of the bike need it). That should help it to roll a bit better.
EDIT:
http://www.diamondback.com/items.asp...temid=110&va=0 - I found that with a google search; is that your bike? If so, it looks pretty heavy. It might not hurt to get a hardtail (only front suspension) if possible, since those are generally lighter, and *much* easier to climb with. The difference for climbing is crazy between my Specialized Hardrock, and my friend's 50 lb Walmart full suspension beast
