You should read the faqs on the fpsc home page, but I will paste the here for you.
Quote: "1.Q: What copyright issues will there be with games I make?
A: In a nutshell - none! You will be able to save EXE files without any restrictions or water-marks / splash screens. These can be given away for free, or sold. There are no commercial restrictions on the sale. If you make a killer game and earn thousands from it you don't owe us a penny. You can sell the games on your own web site, or you can sell them to a publisher, it's up to you. Please keep us informed though, we'd love to hear about it!
2.Q: Does the "no royalty" license include games created by modifying the game engine source code you've released?
A: Yes. There is only one restriction regarding the game engine source code - and that is you cannot use it to create another "Game Making" type of application. But other than that, you can do whatever you like. "
I might be off on this, but if I remember right, if you edit something in a model pack and want to say give it away then you must contact the author of that pack or contact Rick or Janet to make contact reguarding redistribution of the models in the pack or packs.
Obtaining permission is a sure way of staying out of the copyright problems with anyone. Some may put a price tag on it,while others may not.
Also if you are making a game not using fpsc, they do have stand alone packs which still allows you the rights of using those packs.
I leave with one final thing to say. Permission is the key. If you don't know if something is copyrighted always ask the source, but if the source cannot be located or is no longer in service then I would say use at your own risk or don't do it at all.
I hope this helps, but then again I could have read this post wrong.
