I have to remember to take a look at forge.mil, etc. the military seems to be getting on board with free and open source software.
A number of OSS projects are worth to check: Delta 3D, OpenCPI, FalconView, OSSIM
(more at: http://slashdot.org/)
And on simulation, slashdot.org has a cool post on the use of Second Life for Med training:
"... medical schools like Imperial College London are starting to use virtual hospitals in Second Life so students can learn their way around an O.R. before they enter the real thing. ... SL can also expose students to situations that a standard academic program can't duplicate: 'You can take risks that aren't safe in the real world and teach more complex subjects in three dimensions,' says Colleen Lin. ... "
(full article at: http://slashdot.org/)