There must be scores of methods of controlling an Arduino via a PC - however most of them don't present a relatively simple interface for the end user. However with the tutorial by #ben, you can have the framework to create a pleasing browser-based solution using Microsoft Visual Studio. With this a simple web page has been created and code to control four Arduino digital outputs. The PC side simply sends serial commands which the Arduino interprets and acts upon.
The example is well written and digestible, so visit the tutorial to get started. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
If you're new to Arduino, the first step is a solid board for your projects - our Freetronics Eleven - the Arduino-Uno compatible with low-profile USB socket, onboard prototyping space and easy to view LEDs: