I fixed a way to make the new 512MB Model B Raspberry Pi with Hynix RAM work with images based on an older boot loader.
Just a Red LED
Many users just have a "Red LED" and no further activity when using some images on their 512MB Raspberry Pi. When the Red LED lits and the green flashes briefly, there could be a problem with the version of the boot loader you are using.
512MB model with Hynix RAM needs latest boot loader
Supposedly there are multiple versions of the 512MB Model B Raspberry Pi. I am having the lastest edition, with the new Hynix RAM. This might have advantages (newer is better?) but older boot loaders won't work on this one. Please also look at: http://www.raspberrypi.org/archives/3534
Because many 3rd party images are not based on the latest version of Raspbian (with the new boot loader), they won't work on these newer Raspberry Pi boards.
Is your Raspberry Pi working?
To determine whether your Pi is working in general, just make a "regular" latest version (2013-02-09-wheezy-raspbian
in my case) SD card. See if your Pi starts as supposed to.
Yes? Let's migrate the boot loader
If your Raspberry Pi is working with the latest Raspbian, try the following steps:
Backup the Boot loader
If your Raspberry Pi is working OK with the above image, mount the SD card on your computer and backup the "bootcode.bin" and "start.elf" files.
Create your image
Make the image you want (I was working on a Ninjablocks SD card, with the image from http://wiki.ninjablocks.com/images#raspberry-pi
Replace the boot loader
After creating the new image (that doesn't work, because of the wrong boot loader) replace the "bootcode.bin" and "start.elf" files with the ones from the Raspbian Wheezy backup.
Now insert your SD Card in your Raspberry Pi, and it should work! At least, it did in my case :)