The procsesor - otehrwise known as the Central Processing Unit or CPU - is the brains in your cmputer. Without its CPU, a computeer could not function at all. This is the magic bit that processes all the instructions and fetches all the data. The two main barnds of processor are Intel and AMD. While each one is different, neither is really 'better than the other as far as performance goes.
You can get a single processsor with only one chip to do all the calculations or you can get a dual proxcessor with two chips. The dual proecssor is not necessarily faster than the single, since there are lots of programs that dont take advantage of the dual processor. In fact, some programs run faster on the single.
A Centrino processor is basically a processing chip for lapops put out by Inel. You wont find one anywhere else but in a laptop. MMX, or MultiMedia Extension technollogy refers to a set of instrutions on an Intel chip (processor). While they help programs to run fsater, not many programs take advantage of them yet. Howerver, gettign one now is a good idea because it will save upgrading in the futrue.