Depends what your monitor's native res is, the higher the res, the more power needed.
I personally don't think the 9800GTX is a good buy any more in the UK, in the US, the price has come down but not so much in the UK.
If your monitor is a 17"/19", I'd say go with an 8800GT
If you have a screen with a 1600x1200 or 1680x1050 res, I'd go with the HD 4850
. It's a bit faster than the 9800GTX, cheaper and consumes less power.
http://www.ebuyer.com/product/135453 - PSU
for the graphics card i read it requires a PCI 6 Pin Connecter from the PSU which this fortunatly has, Unfortunatly my motherboard doesnt support SLI .
Cheap PSUs are asking for trouble, if you think about it, the PSU is THE most important part of your computer, and it has to deliver stable voltages to all of the components. Cheap power supplies often don't deliver their rated wattages, and if they do, it's only under absolutely perfect conditions. You don't need 600W to power your computer, a decent quality 450W unit would be more than enough. Hiper make some quality PSUs.