What you want is to build a custom kernel. The 2.4 linux kernel is available at:
ftp://ftp.kernel.org/pub/linux/kernel/v ... 4.6.tar.gz
They probably also have the source for 2.6 kernel, I just do not have the 2.6 links.
Then you would have to patch it for what would fit the raspberry pi hardware and chips. Not an easy feat.
But anything with a 2.x kernel is going to be so old that it will be hard to find other up to date and newer software for it.
I know there is a lot of open source software and custom 2.4 and 2.6 kernels for the Zaurus PDA built by Sharp which use ARM processors, have no idea if you could port any of those to run on the Raspberry Pi.
I suppose you could ask at the Zaurus forums at OESF if anyone has considered porting one of the Zaurus distributions to the Raspberry Pi, I have not seen anyone there mention the Pi yet. http://www.oesf.org/forum
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