Building puppy is easy.
First you need to have a working unslung development environment.
Retrieve the unslung sources from CVS:
Change into the unslung working directory:
Build the toolchain, which includes the crosscompiler and other tools. This will take quite a while and will download a large amount of data, but is only required once.
I found that make toolchain failed with the version for CVS above, but succeeded using the instructions at http://www.nslu2-linux.org/wiki/Optware/AddAPackageToOptware.
All that remains, is to build puppy:
You can then copy the resulting puppy package to your slug:
and install it: