Hello b ciprian,
The trick to keeping a CPU or Graphics Card from overheating is to be able to supply the largest amount of cool air coming in. I have gone as far as using a Dremel to router holes in the side of a PC case to add more fans.
Typically I like to have (3)three 80mm or 120mm intake fans in the side panel, (2) 80mm or 120mm fans as exhaust fans. I even remove the front panel to see how many and what size of Intake fans I can put there.
With almost every graphics card that I have used or installed, I have always added a 3rd party VGA cooler. Most of the factory VGA Coolers are mediocre at best. When ever I install a 3rd party VGA cooler, I always use Arctic Silver 5 Thermal Compound which is 99.9% Silver
, which goes between the VGA Cooler Heatsink and the GPU(graphics processing unit).
You can also buy rather inexspensive heatsink kits(applied with thermal tape) that you can attach to the memory chips on the graphics card itself.
I also replace the factory thermal paste that is used for the CPU heatsink/fan with Arctic SIlver 5.
While I am at it, I buy a heatsink for the southbridge, and sometimes the northbridge, as well. Since this is a VERTICAL application, you really should consider using Thermal Tape or Thermal Adhesive. You can use Thermal Adhesive for the Northbridge and Southbridge Heatsinks ONLY. DO NOT use thermal adhesive on your CPU or VGA Cooler
Here are some nice VGA memory heatsink kits from Newegg.Com
Here is Arctic Silver 5 Thermal Compound:
Here is the link to the CPU heatsinks. Just find the one that is compatible to your motherboard.
Here is a HIGHLY RECOMMENDED item. This is the VGA cooler that is compatible with the HD 4850/70/90
And here is a link for a fairly universal VGA cooler. It costs less but I've had it on my card for one year now and love it. But your card runs A LOT hotter than mine so I would choose the one above.
Here is a link to case fans. You really shouldn't buy any fan that is over $8.
If you order fans for your case, they should come supplied with the 4-pin Molex adapter for the PSU. If not, your local PC repair shop or places such as RadioShack should have them.
I think I covered most of the bases. Hope all goes well for you.