After trying all kinds of methods without seeing Debian running on my 500G mbwe (blue light, single hard drive version). Since I don't have a serial cable, I can't see what comes up at boot time to debug. Angry and frustrated, I decided to try this dirty trick to see what kind of hybrid monster would boot (if it would boot at all). But it did boot up and works fine as Debian Lenny! Strange. Hopefully I'm not the only lucky one trying this trick.
This is what I did to have Debian Lenny working on my single hard drive 500G mbwe.
Open the mbwe box and connect its hard drive with stock firmware to a Linux machine.
Connect a new hard drive to the Linux machine. This will be used as the hard drive with Debian Lenny for the mbwe box. You can try it on the stock hard drive if you don't mind the risk of losing data on it.
dd the first 10GB of data on the stock hard drive to the new hard drive.
Connect the new hard drive to the mbwe box and see if it boots. Ping it and log in to see if it works OK. If it does, that's good.
Take the new hard drive out and connect it to the Linux machine. Mount the first partition of the new hard drive. Back up the files in this partition to a safe location, then delete them all. Now the first partition will be empty.
Download these files (To Mario: Thanks mate!)
and extract them to the first partition. Having done that, disconnect the hard drive and connect it to the mbwe box. Prepare to be excited (or utterly disappointed).
Moment of truth. Boot the mbwe box. No light will come on telling you it's ready. Just put your ear next to the hard drive and check if it's cranking. Also try to ping it, check your router to see if it has given the mbwe an IP address, use AngryIP to scan your whole subnet, or do whatever it takes to find the IP address of the mbwe (if it gets one). If it has an IP address that you can ping, you're in business! ssh that address with username root and password mybook will let you in.
If the above sounds like a lot of words, I'll make it simple. All that needs to be done is to remove the original file system on the first partition and replace it with the Debian Lenny file system compiled by Mario.
The reason I made the instructions vague is because I don't know if it works for anyone other than me, so I want more experienced users to have a crack first. If the success rate is good, then more detailed instructions will follow.
Good luck. I hope it works because I'd to say I've given something back to the community.