i am going to buy a phenom ii x4 965 and ati raedon 6770 ddr5...my cabinet does not have any extra fan...my smps is corsair 430w...should i need an extra case fan....my room is not air conditioned..?
check your system temperatures with a tool like PCWizard. The important ones are your CPU temp, GPU temp (in this case you do not have one), and your ambient temp/mobo temp. CPUs and GPUs can get up to 90*c with no problems (granted I would not want to go that high personally... but it should not damage anything until you get above 90*c). Your mobo temps can get up in the upper 30*c range with no real issues (again, would not want to go that high, but you can). Running things cooler will extend the life of your hardware, but things are made to run a little warm with no real issues.
Lastly keep an eye on your room temperature. If your room temp gets above 80*f then it is time to invest in an AC because your heatsinks will not be able to properly disapate heat, and most electronics are not intended to be used in a hot environment (I work in a warehouse, and we are looking at knocking a hole in the wall to put a dedicated window unit for the server because it easily gets up to 110*f in here without AC, and the AC for the office has a hard time keeping up with the building heat + server heat).
Lastly, adding fans is generally more about your tolerance of noise level than they are about cooling. Yes, you should have 1 fan in front taking air in, and 1 fan in back taking air out just to have consistent airflow, and that is enough for 90% of systems out on the market, but if you are OCing (which it does not sound like you are doing), or if you are running multiple GPUs (which you are not doing), then you would need more than a simple 2 fan setup.
Personally, I HATE computer noise. I use a computer for most of what I do throughout the day (work, my other work, my side business, and pleasure). I do a bit of audio and video editing, and I hate system noise as it masks other sounds that I may need to hear. So to remedy this issue I have 2 intake fans (one top, one bottom), 2 outlet fans (one on case, and the other in my power supply), 3 GPU fans, and 2 CPU fans. All of these fans run at 800rpm or lower which means that you cannot hear them. None of them push a ton of air, but it just keeps fresh air always moving through the system, and the only noise I hear in the system are my HDDs which will (some day) be moved to an external system like a NAS in another room, and be replaced by a silent SSD. Does my PC need 9 fans? Nope, it ran cool enough with 4 (CPU, GPU, front intake, PSU outlet). But because I wanted it quiet I went through some extreme measures to shut things up.