How to Turn On An LED via Wireless Network

At the absolute highest level, I want to be able to click a button on my computer and an LED turns on somewhere else. Breaking down the problem, one approach might be to have a server that controls a com port using php and then a client computer might load a webform. Any other feasible methods?

For my idea, I haven't a clue where to start with the php script. Can anyone link me to external libraries I can just download (and not sign up for anything) with good API documentations? Or does php itself provide an API?

012anonymousxyz: an LED turns on somewhere else.

Where is the 'somewhere else'? Is there an Arduino there? How is it connected to 'my computer'?

There are two computers that are both connected to a network. To one of the computers there is an Arduino connected via USB cable. That is all we are working with.

As for which is client and server, I outlined how I thought it might work above. And here is one thing I want to avoid: I don't want to have to reload the page each time I click the button if at all possible. I just want to click a button or press a key, and the LED will reverse states. If the page MUST be reloaded, I'm okay with it, but I really want to avoid that.

Any ideas?

I'd go for Firmata for the Arduino side code and the interface to it.

You can control that (and other things) from a Processing front end, and you can run Processing within a web browser.

In other words, you can probably achieve this without needing to write any code.