Overclocking the gpu

Well first off get something like msi burner to overclock it   or unless you got a program with your GPU. The risks arent too high if you know what your doing, just go as far as you feel safe and small jumps at a time and test, repeat till your happy   In regards a power supply   it will draw more power form the GPU but generally if the power supply is running the computer smooth you'll have enough left for some small overclocks but you not knowing the brand doesnt sound good and its only 400W and you have a quad core already on it but i'm no expert here now but you should have a small bit of headroom for a small overclock  

Question 1: Depends on how much you overclock. Generally, anything less than 5% overclock and the stock cooler give will be just fine.

Question 2: System stability is the main risk factor.

Question 3: You don't need a better mobo to OC a GPU. 3rd party software work fine. PSU, maybe, then again how much you OC it.

Question 4: Upgrading a mobo is a pain in the rear. Not suggested for beginners, also keep in mind upgrading a mobo is by Windows definition "a new PC" therefore you'd also have to buy a new Windows Operating System. Upgrading a PSU is much easier, just about getting right cables in right places.

OCing crap only gives you hotter crap. If you want something faster, buy it.

thanks for the info, it helps