ProSystem is the best emulator of Atari 7800 game console, running on Windows system.
It has been written by Greg Stanton, see http://home.comcast.net/~gscottstanton for details.
Here is a port on GP2X of the version 1.0 that i had previously ported to PSP.
How to use it ? Everything is in the README.txt file.
Here is a full working binary version :