what graphics card???

hi,
i got robbed buying a pc system and it came with call of duty 4 and crysis,and they dont work!!!
my system-am new to this-
processor-intel celeron cpu [email protected]
memory-1.00gb-am going to upgrade that to 3.00gb if poss!
graphics-intel 82945g express chipset family
gaming graphics-250mb
hard disk-147gb
manufacturer-dixonsxp????-bought off the shelf as last one in shop!
model-esystems ei 207
type-32 bit operating system
64bit capable-yes.

crap a know and a paid over £500 for this,must have seen me coming,
what a want to do is upgrade the graphics card but where to start?,
i really fancy the xfx 9600 gt oc 512mb but costly price for it not to work,or a nvidia 8800gt or 8900gt....unknown but hoping you guys can help.
my memory slots have 1 free so will a be able to upgrade to a 3.00gb and does the memory cards have to be of the same make????
help......

you would have to find out if ur motherboard has a pci express slot to buy a newer graphics card. Do you know what motherboard it has?

Also, did you buy your monitor, keyboard etc seperate? or did they come with the pc?

ps how much are you willing to pay for a new graphics card? my bro has this one & can run cod4 at max settings minus soften smoke edges:
http://www.ebuyer.com/product/143338

if this helps,a think av to upgrade my system alot,it all came as a package but think inside stuff is full of crap.