Legality of using doom2 resources in doom

Can I use doom2 resources in doom, or do I need to take the resources from FreeDoom? (Because boom allows stuff from doom2 if given the proper sprites)
Similar topic but not exactly the same
http://www.doomworld.com/vb/showthread.php?s=&threadid=40574

I think this is being discussed here at the moment.

The alpha of doom was NOT RELEASED and NOT COMMECIALIZED. (Well the second is implied by the first but...)
However, Doom2 was released commericially. And yes, I saw the threads. I got no definitive answers.

Each game is a separate product (even though they are sometimes sold todether, such as in the Anthology and in the Collectors Edition). You can use resources from a game in a PWAD if they are already in the corresponding IWAD. Hollenshead clarified this to the KDiZD team when they asked him, and that's why the KDiZD team didn't use DOOM II's Hell knight and SSG, for example.

Obviously some people have infringed the EULA in this respect and they aren't floating dead somewhere, but if you want to stick to the copyright owner's requests, then use commercial stuff only from the game you're modding for.

So all those Doom II maps with Doom 1 music or skies are illegal?

I suppose final doom would complicate things a bit?

Not if you're making a PWAD for either Final Doom game I suppose.

Final Doom adds like 10 textures, tops. Why you'd want those for a non-FD wad is beyond me.

Adds some, modifies many

...and uses Doom and Doom2 music.