What else could it be? If my heater core is fine, what else could it be?

My 1999 oldsmobile bravada has major issues! I pinpointed a leak in it to inside the dash. Now, it's not leaking on my carpet, just pouring out on the outside of my car, but when I am moving, and the heater is on, it sounds like running water inside the car. The windows fog over ferociously, and it smells of antifreeze, and I get no heat. I disconnected the hoses at the fire wall and attached them together. This gave me some extra time until I could come up with how I was going to pay the outrageous shop bill. But, here it is, getting colder and colder, and I need my heater back. So, I asked around, and everyone says its my heater core. My question is that it's not leaking out on to my floorboard, just draining out by where my penger tires are, is this really the heater core, or could it be a bad hose going to the heater core in the dash. The only reason I am worried about this is because I, the dumb girl, have decided to do it myself, and I'm about ready to tear my dashboard out, and get inside. I'm just hoping that this is my heater core before I make a big mistake. Any help would be greatly appreciated. I do have the Chilton Manual on my vehicle, and I'm pretty handy, I just don't want to ruin anything. Is there a way to test the heater core? I checked the hoses on the firewall one time, and they were both equally warm. Any help?