I think the current limit is 32 cpus. Played with a quad p3 years ago and was fun. Currently using a dual amd on 2.6 kernel. Some of the things to show off is if the kernel supports your basics of video card and enable the logo then when you boot that kernel there will be a little penguin for each cpu seen. Also one benefit when building the kernel use the -j8 option for a quad system ' make -j8 ' and the building of the kernel will be about 4 times faster and better. Other wise a normal make will do a single line of make, finish, start the next step on the next cpu and so on if the kernel you are running already is smp enable of course. With say -j2 it starts a line of code and puts the next in a buffer. When down the next one ready to go. A bit faster on a single cpu. So on -j8 it starts 4 lines of code, one for each cpu, and puts 4 in buffers.