Thanks Tekkencode and natx808 for your replies.Sounds like I better go with the Raid 10 set up to be safe!
The Drive which I am considering is:Western Digital Caviar Black WD7502AAEX 750GB 7200 RPM 64MB Cache SATA 6.0Gb/s 3.5" Internal Hard Drivehttp://www.newegg.com/Product/Product.aspx?Item=N82E16822136794
64.99 each x 4 (although I will buy 5x to be safe :P)
If there is another drive you guys could recommend or perhaps this WD Black listed above is not worthy, please let me know as intend to buy this complete set up tomorrow.
Thanks again for all your help