You probably don't need to cross-compile, if you already have an x86 Linux machine to develop on. Often, you can even grab pre-compiled binaries from RPMs. Binaries (and the necessary libraries) from Redhat 6.2 should work. The binaries and libraries from my Mandrake 8.1 machine seem to work also.
In fact, I compiled fbi straight away by just doing the standard ./configure & make (although I did tweak the config.h file to eliminate the X stuff to save space). It needed libjpeg & linungif, so I just copied those from my Mandrake /usr/lib/ folder and put them in the root/usr/lib folder in the build kit. They seem to work fine. (although this probably not be true for everything)
As for making the image, just run the build_16M script in the build kit. It takes stuff from the root/ dir and the kernel from the kernel/ dir and makes your image. (Which will fail if you try to add too much stuff.) Ingo wrote that script and it works great.
If you get a samba client working, let me know and I'll add it to my image. Note that, to test a binary, you can copy it to /tmp and try to run it. But, if you are missing libraries, there is no easy way to add them without rebuilding the image. Putting them in the same dir as the binary might work. Once you know what you need, we can make a new image.