Moo

well the drive is still functioning physically so id consider yourself lucky because its only a matter of time before the heads crash consider yourself even luckier if you have enough time to make a backup of your data you will have a much better chance of succeeding if you do this from a live linux cd ubuntu for instance http://www.ubuntu.com/download/ubuntu/download rather then windows. Keep in mind its only a matter of time, before the heads crash which are responsible for reading and writing your data and you will need the whole head assembly replaced, depending on how much data you have you may be much better off doing a bitstream image of your hard drive, rather than just trying to copy whatever it is directly onto a backup drive. This will make the drive seek all over the place at lightning speed, whereas a bitstream recovery will slowly move the actuator arm which the head is attached to from one end of the platter to the other and skip if a sector is bad then try to slowly read it backwards. Data recovery as Ken mentioned is very expensive so if your drive completely fails and you cant afford to get recovered professionally, you might like to try the old pop it in a antistatic bag and ziplock bag then stick in the freezer overnight trick to get 1 LAST CHANCE.

Specs out nicely however you may like to keep in mind that video card in its x16 slot is going to essentially leave you with 1 standard pci slot for expansion/addons as it will use two slot spaces. you may also like to consider a radeon hd series card that will run cooler then an nvidia, didnt look into your power supply much but you could probaly run that system nicely on about 650 watts so 750 should fit the bill nicely just be sure its 80 plus bronze certified has suffucient molex connectors and ideally single +12V rail design keep in mind a good quality power supply already affords you a reasonable amount of overcurrent protection, and have some noise filtering.