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.
I'd like to add something to point 3:
With a 7950 if I recall correctly the best hashrate you can get would be around the 700 to 800 MH/s mark.
So if he does not mine constantly, because mining while gaming is DEFINETLY NOT advisable when GPU mining about a year probably a lot more is a much better estimate on mining a full BTC. Not to mention that the GPU's power cost will eat that all up almost completely. I am currently hashing at 3.1 GH/s combined with two Antminer U2s and calculated about 6 to 7 months until they've mined me a full BTC.
I strongly recommend to NOT mine SHA 256 coins (Bitcoin, Namecoin, Devcoin) using a GPU. You are better off connecting your GPU to a multipool that is mining scrypt coins and converts them to BTC automatically.
Also I currently wouldn't advise to invest in asics unless you have lot's of spare money to buy big ones and get electric power cheap.
What I'd do if you really want get into mining:
Start off with scrypt multipools as I have suggested. Convert the altcoins you mine there into Bitcoins and use those Bitcoins to buy GH/s on Cex.io or to do daytrading.
While you do that become an active an constructive member in this fine community and take advantage of the signature campaigns and provide paid services for bitcoins. Every now and then someone's looking for a translator.