I would like to install Lion on a different MacBook Pro in my house, but I can't download/install OS X Lion as it hasn't been linked to my Apple ID. Any suggestions?
I think there is a part on booting up a new mac for the first time where it asks you to register with an apple id. If you haven't done that, check in your home folder for something that is a shortcut to register with an apple id. If you already deleted that, or it isn't there, try adding a apple id in the "Accounts" section of system preferences (under your picture and name). After you register, Lion should appear under "Purchased" in the Mac App Store, which you can redownload on other machines.
Well, apart from the obvious solution of simply spending the bucks for Lion in the App Store so you can then legally put it onto all the Macs you own in the future, you could try the following:
Backup the old MBP (duh!)
Connect the two MBPs via Firewire
Put the new one with Lion into Target Disk Mode (reboot with the "T" key held down).
Boot the other one from an medium other than the main boot drive, like an external harddrive or even the Lion MBP you just put into TDM (I think that should work as well). You can do this by connecting the other boot medium before booting and then hold the Option (Alt) key down during boot. You then get a menu where you can select the desired boot drive.
If you have booted into that alternative boot medium, use Disk Utility to wipe and reformat the usual boot drive of that MBP.
Then you could use something like Carbon Copy Cloner to then copy the boot drive from the new Lion MBP over to the usual boot drive of the old MBP.
Finally, select the new Lion boot drive on the old MBP as the default boot drive and reboot.
Sort of complicated for my tastes, but I think that would work. Remember however, that at that point, you have copied over the entire Lion installation from the new MBP and your old installation is wiped out (backup notwithstanding). Thus, you would then have to restore all the files and programs you want to reinstall from your backup, which would take additional time. For a true upgrade installation like you could do with the Lion version from the App Store, you would have to try another solution than mine.
Hope this helps.