After playing maps like SM64 zombies and Battle for Bikini bottom zombies, something piqued my interest. How have these maps been ported? While playing SM64 due to technical glitches, you can definately tell the map is a port rather than a recreation. How is this done? What programs are involved? Any answers would be wonderful, thanks.

Not sure how those specific maps were done but there are lots of ways to get models/textures or geo from games.
Ninja ripper for some older games.
Umodel for most Unreal engine games.
Johndoe (user on this site) has tools and a tutorial for converting source engine maps to codwaw.
Xentax forum is worth looking at if your interested in learning about the process.
Zenhax is another forum thats worth checking.
I think i read somewhere you can use a program while running an emulator to get some stuff from other systems games.
With the exception of Johndoe tools most things need to be put back together manually in radiant.

the problem with importing whole houses or foliage or bridges anything epic you might find you have to manually clip, i think i spend like hours trying to clip the jellyfields part of the spongebob map that had a jellyfield part lol was long time ago but if you dont mind spending some time making the clips and find it theraputic just start finding tons of models to import haha but making it all from the reference inside of radiant might be a quicker process given you can build what you see in a picture for instance


 

Thank you guys both so much for the answers.