It completely depends on your video card. CPU mining isn't very powerful. If you have a decent ATI card, you can mine bitcoins and litecoins at a slow rate, though litecoins will mine faster, and the others even faster than litecoins. If you are restricted to CPU mining, I'd stick to litecoins and use a scryptminer. Bitcoins take a *lot* of computing power to mine and require a high end ATI video card to mine, and even then you'll want to mine with a pool.

I mine Bitcoins with one card, and Litecoins with my other ATI video card. I also use some CPU mining for litecoins as well, but they are super slow, but while I can still get a tiny bit of litecoins with CPU mining, don't bother to try to mine bitcoins with your CPU.