You can get away with a 36GB raptor as your system Hard drive ($103) http://www.newegg.com/Product/Produc...82E16822144200
for your OS and a couple games. The 74GB raptor is $50 more, But it has twice the storage.
Then you will need a 2nd hard drive for storage, (250GB $89) http://www.newegg.com/Product/Produc...82E16822144417
You can use any hard drive as your system hard drive, The WD raptors are fast, If you want Windows and your games to load 30 seconds+ faster then get a WD raptor as your system HDD, If you don't care about 30 seconds, just get 1 250GB HDD for you computer.
The down side of The raptor HDDs...
Serial ATA150(big flat gray cable)
they run hot
they cost allot