If you have an iPad and would like to extend you desktop this is the way to do it.
For a very limited time you can get DisplayLink for free, not sure when this offer will expire but why wait, get the PC version here now.
And you can find the iTunes link here.
I do use my iPad to extend my desktop, like when using Photoshop I dumped all my tools into my iPad so that I had the entire laptop screen to view my images as large as possible.
Because my laptop screen is color corrected and my iPad is not, I actually put Lightroom (the program) on the iPad and have the image I am editing on my (color corrected) laptop screen.
I know that someone out there is going to say "my gosh Scott, you are really old", they might also say "an iPad is a pretty expensive second monitor".
Just a couple of things I'll say to that, if you add the cost of a second monitor AND a dual monitor card you are are going to exceed the cost of an iPad. A dual monitor setup is just that, two monitors.
An iPad will allow you to have a dual monitor setup and much more, not the least of which is a mobile office. It is your marketing tool on the move by allowing presentation of your work ANYWHERE, and many other things, not the least of which is to have a client sign a contract (right on the iPad) regardless of where you are.
Below is a very short (3 minute) demonstration/review video showing DisplayLink in action.