Well, let's start by understanding why it is doing this.
The reason iTunes comes up should be obvious -- it's for syncing the iPad.
The reason iPhoto comes up is because there are pictures on the iPad that have not yet been synced to iPhoto. If you're using iPhoto (and you probably should be), import the photos and then it will stop doing that (until there are again photos on the iPad that aren't synced, of course).
If you're not using iPhoto for some reason, then the next time this happens simply quit iPhoto. Then (while the iPad is still connected!) open Image Capture, another program on your Mac.
Image Capture can ALSO import the photos, but that's not why I'm telling you to open it. At the bottom left of the Image Capture window is a preference that is set to open iPhoto whenever "this device" (the iPad) is connected. Change that to your preferred photo app (or nothing -- but be aware of the consequences of doing that!) and then quit.
Again, the only time a photo app will come up is where there are photos on the iPad that haven't been synced with the computer. Once that's done, iPhoto (or whatever) won't come up when you connect to iTunes.
