Do you need legal permission to make a total conversion of a game? I''ve heard of a few projects that claim to be total conversions of Quake or Unreal Tournament, but was wondering if you need permission to do so since you''d be using those games'' engines in development. Or are people referring to a mod when they say "total conversion"? Just want to know if there are any legal obstacles involved. Also, if you were to make one, and it was for the sole purpose of learning and taking a stab at game design, would you be allowed to do so without having to jump through any legal hoops?

Generally (and I know this specifically applies to both Quake 1/2/3 and UT, which you mentioned), you are free to make and distribute the unique content for a total conversion of these games. However, you are NOT allowed to sell such a conversion, nor are you allowed (for sale or for free) to distribute the base executables for the game''s engine. So, anyone who downloads your total conversion must already own a copy of the respective game.

You should also be careful about what you convert the game into, and steer clear of any possible copyright infringements. Many mod-makers have spent effort creating a game mod based on a popular movie, etc, (eg. Alien TC) only to be threatened with a lawsuit by the owner of the property and forced to stop their development.

When they release the SDK (System Dvelopement Kit) This mean than they let pepeoles do total conversion.

But you can''t seel your conversion or make money from it!