No I want to put them both together...side by side...and use as one big screen. sorry i wasn't very clear about that was i?
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ah rats i forgot my thunderbolt at the office. i bet that is how you do it. otherwise i imagine there would be a lag. i have seen one other person do this on his desktop and laptop (both mac).
As I understand it, it ONLY works with iMac desktops. It's a hardware feature, the iMac is basically 'built in' to an Apple Cinema (or Thunderbolt) Display. Setting it in target display mode basically turns it back into a display, instead of an iMac. I could be wrong, but that's how I understand it. I don't believe the same is possible on the MacBook pro (a physical hardware connection to it's display in such a way).
On the iMac, you can plug another mac directly into it's display, bypassing the iMac hardware. With the MacBook, the display is connected only to the graphics card and there is no way to 'pass' the signal through. Think of Target Display mode almost like unplugging a monitor from a desktop computer and then plugging it into your laptop, except the 'plugging in' is done internally.
Using Air Display will do what you want though. There will be some lag, but it should handle it just fine. I use AirDisplay to use my 23" monitor as a third display, in addition to the MBP and the 27" Cinema Display, only in my case the 'host' is a Windows PC, but it can be a Mac as well. You'll boot up both machines, run the software on both, and setup one as the extended display, then it will appear as if the MBP was just a second monitor (the extended desktop you are looking for).
By the way, when using Air Display, I would recommend connecting the two macs together using an ethernet cable (it doesn't need to be a crossover cable, your MacBooks will automatically make the appropriate connections), and using air display over that network. That will yield you greater speeds and less lag than wifi. You should be able to do this whilst still using WiFi for internet and other network tasks. (or, connect them both to gigabit ethernet ports on your router, if that's a possibility)
1 is a early year 2011 macbook pro
