Second, since your board has a PCI-E slot it will support most cards, the more important things to check are your power supply and the resolution you will be using, post what power supply you have or the current on its 12V rails and what resolution you plan to be gaming on.
Third, learn some patience its unreasonable to get upset after 12 minutes with no response.
LIST ALL YOUR SPEEECCCCSSSSSSSSS HEEEEELLLLPPP UUUSSSS HELLLPPP YOUUUU!!!
...Seriously, please don't use caps lock when posting stuff, and yea we could help you make an informed choice if you list your full specs as well as how much you're willing to spend/what sort of performance you want. Also, what hunter315 said ^.
o.k i cant see why my spec will help i gave you my boards model number ?? and yes i know most cards now except pcie x16 slots my question should actually be what size graphics can my mobo handle ?? such as 128mb 256mb 512mb 1gb?
like it would be pointless if i go out and spend £200 on a graphics card for like 512mb and find my computer will only take 256mb?? my spec is ( windows xp home, 2gig ddr1 , vga on board graphics at 64mb , on board sound by realtek , amd sempron 64 2800+ , oh and the power supply unit is a only a 185 watt ) , the computer is basic cuz we only needed it for net social sites ect.. now we want it for gaming and yes i know your gonna say well get a way more better board then a asus k8v but thats what we got and thats what we wana work with??
Since your PSU is only 185W you will need to replace that to get a decent graphics card in the system. The Sempron is also going to bottleneck you quite a bit, i dont think its really worth attempting to upgrade that system since you will need to replace the PSU, CPU and likely the motherboard to get support for better CPUs so its basically a whole new system anyway.
The reason we ask for the rest of your specs is because we need them. Since your board has a PCI-E 16x slot you could plug a 4GB 5970 into it, but the rest of your system would limit its performance by a large amount, the motherboard doesnt put memory restrictions on your graphics card like you believe.
your best bet would be to increase RAM to 2gb, find a used dual core athlon 64 on ebay, get a new 450w good brand power supply, then get someting like a nvidia gt240 or better. That is as low as I would go for the GFX card.