The graphics settings are very forgiving in STO. You can slid it right back to minimum for yoru card. It won't look pretty, and youll get around 20fps or so, but youll be able to play. Of course, this depends on the rest of yoru system too.
As for upgrades, it all depends on what motherboard you are using. SO you know if the gpu is integrated, or pci-e/agp.
the card is PCI-E im runing a Athlon X2 4000+ 2gb Ram
Well, you can easily upgrade your card to a recommended one fairly cheaply, however you must take note that your CPU isnt one of the best. It's a low rated one, especially since it's only running at around 2.2 ghz. If your short of cash, you can upgrade teh card to a 7950 or an 8800gt very cheaply, and youll be able to play on low-medium settings at a decent fps.
If you arent short of money, i'd suggest looking for a motherboard bundle, which has a mbo, ram, and cpu for less than 200 £$. A mid range gcard will set up back around 60 ish £$