Power supply V Graphics Card.

Right, down to buisness.
At the moment I am playing clan games (mostly Battlefield 2) on a sub-standard PC.
I recently bought 1gb of memory, and am getting 1 more gb soon (making 2gb).
I also would like a new Graphics Card - I had my eye on the GeForce 7600 GT (AGP as I don't have PCIe)
I have an Intel 2.8ghz Pentium 4 Processor which is resonably good for the game I'm playing.
Now my problem is not the memory, but the Graphics Card (I currently have GeForce 5700 LE which is horrible). This card doesn't even meet the minimum requirements even though I've been playing for 3 months.
I suprised it hasn't melted!
My Pavillon 740a has a small power supply, and I'm not sure if it could take the GeForce card I have my eye on.
Any experts out there - 3 questions:
1. Could it take the GeForce 7600 GT?
2. If it can't would it take a 6800 GTS?
3. If it can't take either, what power output should I get?
If looking to spend less than £80 for both card and power.

Now, when I do have 2gb memory, one of the above Graphics cards and 2.8 ghz Intel Pentium 4 processor, will I finally be able to play BF2 on high settings? Thanks.

Thanks for your time.

When you say not very big what do you mean can you give us a number ? 300 watts?
Mactronix