php - Time remaining until specific time from current time of page load

I have to admit that having not even tried to code this myself this question may be a annoying to some but I'm very surprised that I wasn't able to find a good example on the web of what I'm trying to do. Perhaps I'm just not using the right key words in my searches.

I am trying to calculate the time remaining from now (the time the page loads) until a specific date and time (let's say Wednesday May 11, 2011 12:00PM for example) and display it. I had thought it would be quite easy to find a snippet to accomplish this but no luck so far. Does anyone have some example code they have used to accomplish this before? I don't expect anyone to write this for me from scratch but if I can at least get pointed in the right direction it would be extremely helpful.