As many other answers suggest, don't try to mine Crypto's on your cpu. Its just not worth the effort. And the ROI is extremely less. You would actually be losing time and money trying to do it.
Even Crypto's that were once cpu friendly, have ASIC miners , with which your general purpose cpu cannot compete.
Best bet would be to buy an ASIC Miner and start mining the coin with best time/reward ratio. ASIC Miner is going to cost a constant amount. But the way the speculation is going on with Bitcoin, Your underlying returns will increase.
But Mining becomes difficult once too many people swarm up to mine. hence calculate the ROI, Before taking the plunge. :)
All the best