Im about to buy the next system:
-Intel dual core e6300
-A WD 320HDD(the minimal one, not the green one or something else)
-es3g p31 gigabyte motherboard
-An lg dvd burner
-9800GT gigabyte verison
The PSU im about to buy is SEASONIC 400W SS-400ET , is that PSU can handle the system while Im playing games when the video card is in use? Will it be able to handle oc on the CPU without a problem or I just should take the 500W verison.(I have no intention to buy any other video card and im going to stay with this system for the next 4 years at lest)
I checked my references and discovered the total power draw at a wall outlet (mains) for an entire pc sytem with an Intel Core 2 Quad Extreme QX9770 @ 3.852 Ghz and one Gigabyte 9800GT 512MB version used about 155 watts at idle and 227 watts at load. The Gigabyte version uses less power than the other 9800 series cards offered by other companies.
Other references indicate that a system with a moderately overclocked cpu and one video card will typically use just a little under 300 watts during a gaming session.
Seasonic has a reputation for high quality power supplies that consistently earn high marks in technical reviews. The particular model you selected has two 12 volt rails rated at 17 amps each. You should be okay if you are not going to upgrade and you do not do any extremely serious cpu and gpu overclocking.
Normally I would recommend one of the SeaSonic S12 II series of power supplies, preferably the 500 watt version. A lot of other high quality psu's are based on the S12 series.