So I went with Debian/Stable (Sarge)…
NVIDIA driver (both deb package and original installer) with vanilla kernel 2.6.12.3 makes my laptop freeze after a while => no Twinview/Xinerama yet :-(((
Got backports for the Mono stack from Fromorer of #debian.de fame and for Xorg from Nobse (another debian dev).
Following this howto to get Sun Java 5 installed. Lets see if this works out..