Don't install a fan on a 5450 card. Even if you manage to get a fan assembly really cheap you are going to end up throwing it away because, even if it does lower your temps, it won't improve performance at all.
Save your money and get a Radeon HD 6670 card. It's a nice upgrade and it most likely will not overtax your PSU.
I was saying that i want to install fan because
1). i have overclocked it.
2). Same card is available of HIS(mine is of Saphhire) with fan
3). I watched video where user was playing max payne 3 using this card...and my pc lags a lot