Like so many other Dreambox tasks this sounds easy at first, but can get quite complex
First you need to have a PC that is broadband connected or better.
The build will download a LOT of stuff from the internet as it goes.
Second you will need to get the source. This is covered in detail here http://cvs.tuxbox.org/.
Click on the installation instruction link and CHECK each of the prerequisites are installed and active on your box. This is crucial to getting a good build.
I use Mandrake 9.2, and a number of the utils were installed but not the default (e.g. automake).
Create a directory to receive the source (I use /data/tuxbox-cvs for the source and /data/dream for the output as there isn't enough space in my /home mount)
Then cd to your source directory and fetch the source: cvs -firstname.lastname@example.org:/cvs/tuxbox -z3 co -r rel_1_0_0 .
don't miss that final '.' char at the end.
Once the source has downloaded (only takes a few mins) you cd into the cdk directory.
DO NOT ATTEMPT TO BUILD AS ROOT.
Run the following (substitute directory names as required): ./autogen.sh ./configure --prefix=/data/dream --with-cvsdir=/data/tuxbox-cvs --with-targetruleset=flash --with-cpu=405 --disable-libcrypto --disable-flashmodutils --enable-maintainer-mode