(XPS 420) Upgrading from a Nvidia 8800GT to ....?

Hello there,

I'm finally interested in searching for a new graphics card. I've been searching around for a card that'll fit into the XPS420. I know there are numerous issues with the size of the tower of the XPS and of course the power supply needed.

The budge i'm look at is around £250. I've been looking at the Nvidia 460/470 and the ATI Radion 5870.

Basically, my real question to you guys is: 

• What's the best graphics card available at the price budge I have?
• Can this graphics card fit in the current XPS 420 tower (My current graphics card being the 8800GT is roughly - Length: 9.5 inches, Height: Close to 1 inch)
• What power supply would I need to have to buy in order for it to work?

Having such a slim graphics card to start with, I can't really see how all the new cards such as 4.3 inches, are going to fit in the tower, as the MASSIVE fan is in the way. The length shouldn't be a problem, as i've got about 13 inches of space.

If anyone could give me any information on this, it would be fantastic.

Thanks again,

Chris.