Making a new computer?

Hello everyone. I want to make a new computer by buying parts in Newegg.com. Since I am new in this, I couldn't understand something and I hope someone can answer them.

I bought the CPU and graphic card already.

My CPU: Intel Core 2 Quad Q8300
( http://www.newegg.com/Product/Product.aspx?Item=N82E16819115207 )

Graphic Card: GeForce GTS 250 1GB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card
(http://www.newegg.com/Product/Product.aspx?Item=N82E16814133266&Tpk=14-133-266)




1.) Do I have to buy a hard drive? If yes, is this one:

Western Digital Caviar Black WD6401AALS 640GB 7200 RPM 32MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive
(http://www.newegg.com/Product/Product.aspx?Item=N82E16822136319&nm_mc=EMC-IGNEFL010810&cm_mmc=EMC-IGNEFL010810-_-HardDrives-_-LC1C-_-22136319)
ok with everything?


2.) For motherboard, I got confused a lot. I have picked this one :

GIGABYTE GA-G41M-ES2L LGA 775 Intel G41 Micro ATX Intel Motherboard
(http://www.newegg.com/Product/Product.aspx?Item=N82E16813128388)

Is that compatible to my CPU and graphic card?

3.) I have picked this case: NZXT GAMMA Classic Series GAMA-001BK Black Steel ATX Mid Tower Computer Case
(http://www.newegg.com/Product/Product.aspx?Item=N82E16811146061&nm_mc=EMC-IGNEFL010810&cm_mmc=EMC-IGNEFL010810-_-ComputerCases-_-LC4B-_-11146061)

I want to ask, is that ok with this one? Can ATX-mid tower case hold micro ATX motherboard?

4.) For memory, I am going to take my 4GB ram from my hp desktop (8GB). When I look at the specification of the motherboard, I saw the memory standard is DDR2 800. How do I know if my memory is DDR2 800 or something else?




Thank you so much for answering my questions. I will try to learn from this experience and gain more knowledge.