The problem was with the init scripts. I couldn't get init to read (or appear to read) either init.a1.rc or init.A1_07.rc, so I had the build copy the original init.rc from the stock system to init.rc in the CM7 build. However, this init script wasn't suitable for some reason or other. I noticed that init also tries to read "init.target.rc", so I had the build copy the stock init.rc to that name instead. Now it boots up.
I thought there might be some people who would find it fun to have a play with this early version, so I created a page to host it: http://www.doc.ic.ac.uk/~grm08/ideapad/cyanogenmod/
First build of CM7 for the Ideapad A1. What appears to work: screen, touchscreen, audio, menu/home/back/volume/power buttons. What doesn't work: SD card, wifi, bluetooth, camera, accelerometer. Reboots every couple of minutes. Anything not mentioned, assume it doesn't work.
I've also provided a zip that restores the stock A1 ramdisk:
If you want to go back to the stock system, you will need to install this zip to bring back the stock initial ramdisk. This is for the ROW 2375 build only - don't use it with other builds.
I would recommend against installing this if you don't have the 2375 ROW build on your A1, because I only have provided a way to get back to stock for that build (you could use an OTA package to get back to other builds, but if you want to do that, you're on your own). Do a backup of the stock system before you install. Install from Clockworkmod in the usual way. Wipe data and cache after installing. When you want to go back to the stock system, install stock-a1-ramdisk.zip then restore the backup.
The usual warning/disclaimer:
Since this has only undergone light testing, there is risk of damage or problems due to bugs in the ROM or its installation. The worst case scenario is that your A1 will be bricked. In the event that something goes wrong, I will do my best to help recover the situation, but I am not liable for any damage incurred. It is up to you to decide if you want to take this risk. If you are not comfortable with the risk, then do not attempt to install the ROM!