Can anyone give me a good and simple example of the comet technique using PHP?
I just need an example that uses a persistent HTTP connection or something similar. I
For IIS, there's WebSync. Since you're using PHP, however, you might be better off with WebSync On-Demand. Either one will give you the server-push you're looking for, and is simple to use. Check out this question as well, which is basically what you're after.
Here's a simple example of WebSync On-Demand in action using no scripting language. Simply open in two windows, and see the publish/subscribe in action.
To publish from the server, you can use the PHP api.