No Bootable Device error when trying to install Win7 on a MBP (mid 2007 SR) / Lion
In the end, I couldn't make the machine boot from the DVD. However, I found a workaround that I want to share for anyone with a similar problem: I used VMware Fusion to boot the Boot Camp partition from OS X. I then set up the VM to boot from the iso I made the DVD from (might have worked with the DVD as well, didn't try). After running through the part of the installation where the base system was written to disk and the system wanted to restart, I turned off the VM, booted from the Boot Camp partition and (with Win7 DVD in drive) then ran through the rest of the installation procedure without problem.