The Debian/woody virtual machine provides a Bering source kernel that is already patched and compiled. So most of the steps described below are unnecessary. Just install your virtual machine as explained in the Leaf UML documentation and login. Then any modification to the kernel is as easy as:
mkdir /tmp/Bering_modules_2.4.18 cd /usr/src/linux make menuconfig (make your changes here and save) make dep;make bzImage; make modules;make modules_install INSTALL_MOD_PATH=/tmp/Bering_modules_2.4.18;
The Debian/Woody virtual machine is provided with the Bering-rc4 2.4.18 kernel environnement. The stable version only differs from rc4 in its version of ipsec (1.99 instead of 1.98b) and pcmcia-cs (3.2.3 instead of 3.2.1). So you only need to replace those two packages (if you need them) to have a Bering-stable development environment."
The only thing that cannot be done on the virtual machine is kernel compression through UPX. For some strange reason the UPX binary segfault on the UML machine. That has to be done on the host machine.