1) Yes. Many people without ASICs or USBs do this. Make sure to use your GPU (Graphic processing unit) as your miner as opposed to your CPU, since GPU is faster.
2) Maybe. Computer will probably melt though. I wouldn't count on good mining rates while gaming, unless you use a USB or ASIC miner.
3) Based on hardware... I'd estimate at least a month. For full BTC you REALLY need efficient or fast ASICs. I recommend you mine other crypto currencies, since they are easier to mine for and more profitable.

Sorry if this isn't what you're looking for, and my mining time estimate may be off by a week. Or month. Expect it to take a LONG time.