mirror modifier?

This has got to be the most user-unfriendly application I have ever used.
I am making a model that is completely symetrical. I used the mirror modifier to insure that both sides are identical. No problem there. But when I try to paint it, I can’t. It won’t let me. I realized maybe the mirror modifier needs to be closed before I can applay texture. I close the mirror modifier and… POOF! Half my model vanishes.
Would someone please give me a brief rundown on how to use the mirror mod AND have a whole model when done? I have watched tutorials till I am blue in the face. I swear I hear that guy’s voice in my sleep.
I mean no offense. I am aware that Blender is an excellent program. Many have warned me about how difficult it is to get started using it and they weren’t lying. It seems everything is a morphing combination lock; what works one time probably will not work when you try it again.
I am using Blender 2.56.

OK… This happens to me all the time… Immediately after giving in to posting a question, I figure out the answer for myself.
I did not click the little “apply” button before X-ing out the mirror modifier window.