SLIND and realtime extensions
A friend of mine (Philipp Beyer) is writing his diploma thesis at Siemens about realtime linux based on SLIND (Siemens Linux Distribution). SLIND is a Debian based Linux-System, onto a PXE-bootable embedded device. SLIND supports cross development environment, i.e. the target is not necessary of the same architecture as the host.
He has currently tested RTAI with SLIND and did some measurements. Take a look at his wiki for more information. Next steps would be to compare RTAI and XENOMAI on embedded Linux platforms.