Hi charmedboy:
I have first hand information on the matter, since ever since I was pregnant I began speaking English to my baby, and my husband, who's English is good but not as proficient, would speak to him in Spanish, our mother tongue.
Once he was born, I continued speaking only English to him. It took him about a month or two more than it took my nieces and nephews to begin repeating words; as a first-time mother, of course I asked the pediatrician in one of our monthly check-ups. He mentioned that besides still being on time, my baby would take a little bit longer because he was processing two languages simultaneously.
Wow! No wonder he spent so many years at school! Of course my baby uttered his first words, and incredible as it may seem, he spoke Spanish words to his dad and English words to me.
By the time he was 18 months he was able to ask dad for mano but mom for hand; ask dad for pelota but ask mom for ball, etc.
When he turned 3 we registered him at a bilingual school in town, where one of his kindergarden teachers speaks and teaches in Spanish for 2 hours and then another one teaches the same things but speaking only English for another 90 minutes (after a 30 minute break - of course).
As of today, he is almost five, and he understands everything he hears in both languages. We can go to English-only movies and he will understand what's happening, same with the tv and same with other persons speaking English to him. Whenever he does not understand a specific word, he asks about it, and then I explain it to him and then give him the equivalent in Spanish. If he asks his dad, my husband will explain the word to him in Spanish and then provide the equivalent in English.
I have to mention that he is NOT speaking English, just a few short phrases (may I go to the restroom, please? may I have some chocolate milk, please? I am 4; my name is xxx; and the such). Of course he speaks Spanish with everybody, so I believe that's the reason he really doesn't speak English, but he still has a lot of time ahead, and I think that the foundation has been set.
I've read that this has to start within the first six months, I don't know how true this is but I think it is never too late.
I also relied in some DVDs that present items to babies in different languages. They claim that they "open" the "threads" of brain cells in charge of these type of skills. I think they helped, they sure didn't hurt
Maybe you can try this with some nephews or small children close to you
Greetings
ILT