For those interested (i.e. shameless plug of my own project ;)), I'm working on a game editor that will allow you to create Action Adventures. Definitely not complete yet, but you can already create some nice levels, and add NPC conversations :). http://rpgplayground.com
Nintendo seems to be ok with fan made ports as long as they aren't selling it - as seems to be the case with Mari0 [2].
There was some work being done on porting Super Metroid to the PC but I think that has been lost in time. Many years ago I contacted the author and instead of giving me the source he gave me compiled binaries :(. I can post a link if people are interested.
[1] http://www.zeldaclassic.com/
[2] http://stabyourself.net/mari0/