I don't know for sure, the rules on J2O just prohibit the use of copyrighted material as a whole including 'abandonware' and such.

Most music from other games are from either shareware or freeware games, which is totally fine. But thinking about that, Jazz1 music from non-shareware levels has been included a lot and it's never been a problem.

So I guess it's alright to include music from other games. At least their companies are not as pricky about it as the average music industry richies.

But you'd have to contact Stijn or Cooba for a more definite answer.