If it is a game, you'll want to use something more client-side like JavaScript or Flash.
I'd recomend Flash, simply because it has a full scripting language and is easier to manipulate the visuals than JavaScript. Also, it is easier to detect if someone has Flash and can run the game than having to deal with the big differences between browser support of JavaScript. And, if the user doesn't have version of Flash you use, it is a snap to upgrade it. Not so with JavaScript.
You can still use PHP either way to store scores and player info in a database.
There are several sites that could be helpful either way...
Flash
http://www.flashkit.com/
http://www.ultrashock.com/
JavaScript
http://www.javascript.com/
HTH