1) I'm assuming you mean the SCP (Source Code Project), which is a community-driven effort to bring Freespace 2 from the quality game that it was in 1999 into the current generation of games through improvements to the source. You still technically need FS2 to play, though the dependence on the original install decreases by the day.
2) To be safe, I'd recommend finding the official link to 3.6.5. There are other more stable builds in some regards, but that one has the most of the more recent features and bugfixes, and there's a good bit of community knowledge on its faults. It's also the easiest to install from the ground up.