When I first setup my MBP on 10.6 I made a lot of newb mistakes, and was unable to get Ruby on Rails to install, amongst a lot of other things. Because of this, I decided to backup everything on to a Time Machine HDD and re-install Lion.
I had a bunch of problems but managed to sort them out, requiring me to go back to 10.6 from the original disc that came with the MBP.
Before I did anything however, I burnt the Lion installer that I got from the App Store to a DVD. Now though, when I try to run it, I get the following:
Cannot download additional components.
I've managed to download software updates, so I know it can connect to the Apple servers.