I haven't tried the VGA adapter yet. My thought is that if I really want to be wired I'll just use my MacBook. I've been looking for ways to wirelessly work from my iPad with my projector. Thus far, all my options center upon having a computer attached to my projector. We have wi-fi in our building so I use that as my wireless connection to my iPad. If you don't have wi-fi you might still be able to use these solutions, but you'll need to set up an "Ad-Hoc" network.

This is an application which basically turns the iPad into a giant track pad for a computer. The iPad app costs $2.99 and the application for the computer is free. I've used it with both Snow Leopard and WIndows XP. It's pretty cool. When you connect, a row of icons for programs appears along the bottom of your iPad screen. If you're on a Mac the default is your dock, on Windows it's a program list that you put together. This is very handy for application switching. 

Additionally a set of buttons appear at the top of the screen. These will be different depending on the typ of application you're using. If you're in a browser, for example you get forward, back, refresh, home and such. These buttons are completely customizable as well. You also can pull up a full keyboard when you need it.

Advantages: You can use it with Windows or Mac. It is very responsive. There's really no noticeable lag. You can, of course, use this with any program that will run on your computer.

Disadvantages: If you want to write on the screen you still need a program on the computer to do it. You can only use it with a computer you've installed the software on already.

Approach 2: AirSketch 

For this one I have a video review. AirSketch really is quite awesome! This one really does most of what I need. This one costs $7.99. When I bought it it cost $6.99, but apparently they bumped the price up by a dollar. If you're a teacher it's well worth the $8. Here's a screen capture lecture I did that relied heavily on AirSketch.

Advantages: Works with any computer as long as it has a "Modern" web browser. I've used it with Firefox and Chrome on both WinXP and Snow Leopard. You can zoom the iPad display to allow for much finer writing on the big screen. There's also a free version you can try to make sure it will work on your network.
Disadvantages: You are pretty much stuck with images or pdfs. No web surfing, no videos, no PowerPoint or Keynote. However, there are many ways of converting presentations to a series of images or a pdf file and you could then use them in AirSketch.

Approach 3: AirDisplay

Ok, I've only just gotten this one and have really only "kicked the tires" on it. AirDisplay was designed to act as a second monitor for your computer. Pretty cool in and of itself, but it does cost $10. But Nathan Steves over at teachwithyouripad.wikispaces.com has come up with a way of using it as a wireless connection to your classroom projector. On my home network this works great. However, on our school network I can't get it to work. I really need to sit down with our technology guy and see what we can do. 

That said, I have used it with my projector by setting up an ad-hoc network with my MacBook. I then wire my MacBook to the internet and I'm good to go. It takes a bit of fiddling to get all three displays (laptop, iPad, and projector) to mirror one another but once they do you're in business. You need to go to your Display Settings and make sure the Mirroring check box is checked. You may have to un-check and re-check it.