rar is a compression method that lets you break up a large file into smaller chunks. You'll need to recombine the chunks to form the original file.
UnRarX will work, so should Stuffit.
sfv (simple file verificator), a file used to make sure the archive is whole and not corrupt, check versiontracker for macsfv or the like.
An .nfo file is simply an information flie. Open it with textedit. That .nfo file should give you a lot of details if the guy did his part. Should look something like this:
File : 108.2 Mb (113,432,580), duration 10:50
Video : 1150 Kbps, 29.970 fps res. 352*240 (4:3), MPG1 = MPEG 1 (VCD)
Audio : 224 Kbps, 44100 Hz, 2 chan., 0x51 = Mpeg-1 audio Layer 2
I'll let others more knowledable comment on your other question.
HTH