Multisampling is combing several similar images for FSAA. Supersampling renders the image higher than the current resolution internally and samples it down to fit your screen. Multi gives smoother lines, while supersampling can make textures appear much sharper. Multi is by far the faster type.
rgss was on the voodoo 5, don't worry about it.
Quincunx is sort of a mathematical cheat. Sometimes it gives the appearance of 4x fsaa at 2x speeds, but sometimes it looks no better than 2x and tends to blur textures a bit. The Geforce 4 has a newer version of quincunx (but given a different name) that tends to eliminate that blurring of textures, though doesn't seem to improve over 4x by too much. The geforce 4 has more of it's physical space dedicate to FSAA so there is less of an overhead in speed costs by enabling it.
If you want the details, read Anand's review.