How fast does a processor have to be to mine bitcoins
After the creation of specialized hardware, created ex-professo for mining bitcoins, difficulty has climbed so high that it's not profitable to mine them in anything but an ASIC (if you can afford it). Anything else and you'll lose money or barely pay the electricity consumption.

Plus, it's definitely NOT recommended to do mining on a laptop - having either the GPU or the CPU running at 100% the whole day long produces a lot of heat and will significantly reduce the life-span of components. 

Having said that, if just for fun, you could try mining Primecoin, Protoshares or Quarkcoin some hours a day - they're minable only with CPU (for now). Or better yet: mine a scrypt-based with your graphic card (it's usually much more profitable). Maybe mine dogecoins for 3-4 hours a day - Dogecoin and the dog meme are fun :)

Just don't expect you'll get a lot of any coin mining partial-time.