Motherboard compatibility question

Hi everyone,

I'm replacing the CPU, GPU, and PSU in my desktop and I want to know if the parts I have picked out are compatible with my motherboard.

--Motherboard Name: FIC K7M-NF18G (AU31) (3 PCI, 1 AGP, 2 DDR DIMM, Audio, Video, LAN)
--Chipset: nVIDIA nForce2 IGP

These are going to be the new parts:
--GPU: ASUS EAH6850 DC/2DIS/1GD5/V2 Radeon HD 6850 1GB 256-bit GDDR5 PCI Express 2.1 x16 HDCP Ready CrossFireX Support Video Card with Eyefinity
--CPU: Intel Core i3-2120 Sandy Bridge 3.3GHz LGA 1155 65W Dual-Core Desktop Processor Intel HD Graphics 2000 BX80623I32120

I haven't picked out a PSU because I'm not sure how many watts that GPU requires; any suggestions? Your help is greatly appreciated.

Also, will it be worth the $100 to upgrade from XP to Windows 7? Or will these parts function fine with the former?

-Nick