lamont:Sparticles are also particles. They're particles which are predicted to exist in supersymmetry theories and they mathematically pair up with 'normal' particles like quarks, electrons, photons, etc. The supersymmetric fermions (spin-1/2) particles get a 's-' prefix so they're squarks and selectrions, the supersymmetric bosons (integral spin) particles get an '-ino' suffix instead of an '-on', so you get a photino, gluino, etc. There's good theoretical reason to believe in their existance apart from string theory because electroweak unification has been very successful in uniting the electromagnetic and weak forces, and supersymmetry is just an extension of those theories uniting the electroweak theory with the strong force. Sparticles also aren't even 'opposite' to particles in the sense that matter and antimatter are 'opposites' and annihilate each other (there should also be anti-sparticles, btw).
Branes are just a generalization of strings. Strings are 1-branes. A 2-brane would be a 2-dimensional fundamental object more like a piece of paper...
Wow. Most posts are hard for me to follow but this takes the cake. Did you find this on wikipedia?