Hello Fella

Whats the brand of the powersupply? and the rest of your system specs?

i use cooler master brand and my spec is..
AMD Phenomx4
Asus Motherboard M4A78
2G RAM
Nvidia 9400 GT
CPU cooler z600

ATI 5870 is my future graphic card planning... So i need an opinion.  

Coolermaster isn't the best quality brand for PSU's. But your PSU will be enough for a HD5870.

so... in this case i can buy 550 watt PSU with ati 5870 ya...?

can you suggest me which brand are the best quality for PSU.. i still new in gaming world...

A few good brands:

Corsair
PC Power and Cooling
Antec
Enermax
Thermaltake
Seasonic
Be quiet!

A good quality 500W PSU will be fine for your system

ooo... ok i get it. thank a lot,

i realy need your help in the future... :-)

Your welcome : )