I've just started hacking a 1262 based on the same sources.
So far the only thing of any use is the linux code. It has the "venus" drivers for the vid/audio codecs (+ a few other housekeeping things).
The first step is to try to compile it. My first attempt with a v4 GNU gcc brought up lots of errors. When these were fixed, the result was bigger than the space in the /dev/mtdblock/0 would allow.
So I went back to gcc 3.4.4 (mipsel-linux, of course). It ended up smaller than the linux already in the flash. But I noticed the default .config makes all the dvb code modules instead of builtins. So I checked "y" instead of "m" for all that stuff and recompiled.
Now the resulting linux is only 10% smaller than the flash version. I don't know why the diff now. A comparison of all the extracted strings from the new linux and the old one shows almost all the code is now in there. But I'm taking my time before I try to blow the flash with the new linux.
I also managed to locate the Realtek BIOS up in /dev/mtdblock/4. You need to activate the serial console (on the left-hand 4-pin connector) before this makes sense. Type 2 carriage returns after powerup and you're in something that behaves a bit like U-Boot, but itsn't quite as clean. :)
It's been suggested I blow away the existing linux and root (write-protected squashfs) and put in a uboot, linux and root. But I don't think it's going to be so easy.