It works for all Rockbox ports- you compile it like you would compile a build, just pressing "S" for simulator (instead of the usual "N") when it prompts you...
Read the
"Simple Guide To Compiling".
It may look complicated but in reality it isn't. The instructions are basic step-by-step, telling you pretty much exactly what to type, and once you've done it for the first time it becomes second nature.
EDIT: Sorry, nearly forgot you LGMS
! LGMS compliles a H3xx simulator which he puts up for download in his thread. If you don't want to bother compiling your own, head that way...