radiator help, please

I have a 99 EX with about 97,000 miles and a stock radiator. Recently, for reasons unknown to me, my radiator seems to be either leaking or gobbling up all the 50/50 radiator fluid/water I've been putting in to it. Four times now after coming home from work or sumthinf the reservoir has been virtually empty and just yesterday on the freeway, I noticed the hood smoking a little only to find that there seemed to be only water in the reservoir and that it was boiling (even though I had just filled it up with fluid the night before). The AC was on and it was a little stop and go, but not so much that I think that should have happened. I check under the car often to see if there is any obvious leak but nothing. So, my question is where is the fluid going? Is it likely to just be a radiator problem, or indicative of some worse engine issue? Can coolant actually evaporate? What's going on?!?!? Oh wait, that's kinda more than one question, huh? Well, feel free to answer any or all that you'd like. Thanks so much!

might have a blown headgasket. Is your car smoking a lot?