Try using each of the 2Gb memory sticks one at a time. You may have a
bad RAM stick that's triggering the re-boot. Also take note of the
warnings about ventillation and using memory rated at 85C due to
passive cooling on these boards. Wouldn't exepect that to be the root
of the problems regarding getting Ubuntu installed but it's worth
being aware of it !

www.intel.com/.../CS-032627.htm

It may also be the board is fussy about the memory when loaded to the
maximum it can take. Wouldn't be the first time I've come across
boards that don't like particular brands of RAM !!