No, there is no octo-core processor.
But if you use a 64bit version of windows, you can use 2 physical processors, combined = octo core.
BTW, AMD is busy making an 12-core cpu... Imagina having 2 of those
BTW, I have a Q6600, quad-core 2.40Ghz, and yes, it goes MUCH faster than dual or single core.
Also if you get a Q6600, and build your pc youself (wich I advise), I advise you to install a good cooler over your CPU, and you can EASALY overclock the Q6600 to atleast 3Ghz.
You can even overclock it to 3Ghz with a standard cooler. (problem is I have a dell, and they BIOS is locked, I can't change my FSB clock/multiplier).
BTW, if you do want to overclock, make sure your CPU temperature stays below 50°C, as long as it stays under that your fine (there is a margin, so dont worry if you reach 49 :P )