Running command with browser
On the client side (the browser), you can do it with the simplest approach. Just an html form. javascript would make it nicer for validation and to do ajax calls so the page doesnt have to refresh. But your main focus is handling it on the server. You could receive the form request in the language of your choice. If you are already running python, you could write a super fast cgi python script. Look at the cgi module for python. You would need to put this into the apache server on osx if thats where you will host it. 
Unfortunately, your question about exactly how to write it is beyond the scope of a simple answer. But google for how to write and html form, or look at maybe jquery to build a quick form that can make ajax calls easily. 
Then search for how to use the python cgi module and receive POST requests.
I want to have a "control panel" on a website, and when a button is pressed, I want it to run a command on the server (my computer).  The panel is to run different python scripts I wrote (one script for each button), and I want to run the panel on my Mac, my iPod touch, and my wii.  The best way I see for this is a website, since they all have browsers.  Is there a javascript or something to run a command on my computer whenever the button is pressed? 
EDIT: I heard AJAX might work for server-based things like this, but I have no idea how to do that.  Is there like a 'system' block or something I can use?