Will it work?

Hi, I'm soon planning to purchase a new Video card. I've had this current one for around four years now and I really think it's time for me to upgrade as the FPS on newer games I'm starting to play is deteriorating.

Here's my current stuff:

CPU: AMD Phenom II X4 955 3.2GHz x4 Core.

Video Card: ATI Radeon 4890 HD.

CPU Cooler: Cooler Master Real Power M620 | More info: http://www.coolermaster.com/service/...S-620-ASAA-A1/

Motherboard: Gigabyte MA77OT-UD3P

Memory: Corsair Dominator 4GB (2x2) DDR3

Case: Cooler Master CM 690.

Power Supply: (Not sure on the name but I've got the product code) Cooler Master RS-620-ASAA-A1

OS: Windows Vista Home Premium 64bit (I plan to upgrade to w7)

Display: 22" Samsung Monitor (1680x1050)

Not really sure If I've listed all the required information but any questions you ask I'll try my best to answer. I have around £320 to spend on upgrades, I'm mainly looking for a graphical upgrade and I will be spending around £66 on Windows 7, unless I can get it for any cheaper. I've been looking at one video card in particular, that would be the geforce gtx 660 ti - I'm not sure if my current computer will support this and if it's worth the money. Any suggestions and answers will be greatly appreciated, thanks.