Upgrading Tomorrow, Final Checks!

[Ex7ra]

CPU £157: http://www.dabs.com/products/intel-core-i5-3550-s1155-3-3ghz-6mb-7YXK.html?refs=4294944663&src=2
Motherboard £76: http://www.dabs.com/products/gigabyte-h77-d3h-s1155-intel-z77-ddr3-atx-800W.html?refs=4294943313&src=3
RAM £35: http://www.dabs.com/products/crucial-8gb--2x4gb--240pin-dimm-ddr3-pc3-10600-70JG.html?refs=468550000-354710000&src=3
This leaves around £70 left for a OS... if thats all i need
The things that i am getting rid of in my current PC are: Processor, Ram, Mobo, Heatsink
I have a XFX 650w PSU and a GTX 560ti GPU...
If i buy the things that i listed, will they all work together, compatibility wise?...
Also, are HDD's universal? meaning, work with any mobo / cpu etc..?
PLEASE ANSWER FAST DDDD
Also...
If my brother buys a new psu and graphics card, would he be able to use my old mobo/ram/cpu/heatsink as a starter for building a PC?
then all he needs is a HDD, Case and a cd drive no?

Thankyou so much to anyone who can answer... i just want to be triple sure before i go ahead and order all the parts!

 

[Ex7ra]

It wont let me edit the original post, but the thing that i REALLY would like to know is that if i NEED a new OS, or can I get a new key from PC world, since my one was OEM, and are HDD's universal? Do they work with almost any mobo / processor?