I got than new GeForce 8400 GS video card which is unsupport by Obilivion it put me on medium setting graphic thing. Than I incress the default to hight or keep it medium.

Better keep it to medium, it's not very strong card.

It's more or less compatible with the practical minimum Geforce, the 6600GT, so it won't need the Ultra Low, pure MUD image quality setting that the Gefore 6200, 6500, 7100, 7200, 7400, 8200, 9100, and 7300 GS have to run under.

The Graphic Card that was nremove was than ATI Radeon Xpress 1250.

An Xpress1250 cannot be "removed". It is buried inside of an AMD chipset. It is an onboard, or Integrated, chipset video chip. It was based on the old Radeon 9600 card, which had gone through a metamorphosis from AGP to PCIe, and a name change to X300. It is thus much older than the Geforce 8400, and has far fewer shader units, although for raw speed the two probably aren't that far apart.

Here's what you should have done, for the same cost: http://www.gpureview.com/show_cards.php?card1=529&card2=584

That is a Radeon two years newer, and considerably better. It's not really a Gaming card for TODAY's games, it was just a borderline zone card two years ago, but we are in here talking about a five year old game, for which you bought an overpriced (probably) four year old card that isn't very good.

Here are two cards at Newegg for price comparison, both Gigabyte branded:

Gigabyte 8400 GS 512 MBs RAM $39 http://www.newegg.com/Product/Product.aspx?Item=N82E16814125289

Gigabyte HD 4550 512 MBs DDR3 $40 http://www.newegg.com/Product/Product.aspx?Item=N82E16814125250

There are also still some Radeon HD 2400 Pro cards available for sale, had you really wanted cheapness, those are about as bad as the 8400 GS is, while being priced closer to the value, around $25 or so.

My brother remove that card as it was add to than other visa computer. I than able to play Fallout3 than be able to move around.

The card was make by Galaxy GeoForce 8400 GS.