Where to start.

On a couple of seperate occasions in the past I have had issues booting up my system. It would hang on the WIN XP "blue bar screen" or just go blank after the BIOS page. After much time working in system recovery I couldn't fix anything and had to take my rig to the local computer store. They found bad sectors on the hard drive, flagged them and I basically ended up re-installing windows fresh.

This past week I did a fresh OS install because it was starting to hang like it had in the past. After the reinstall everything was fine for two days (just long enough to re-install all my apps and games and customize all my stuff), and now I get a black screen with the message that my HD cannot be read from. I have tried messing around with system recovery and wasn't able to get anything working again. The most I could find out was the boot sector was corrupted. After all of this I am ready to buy a new HD and start over again. My questions are:

Is is possible to just fix the boot sector on my current drive or is my best bet to buy a new hard drive?
What could keep causing these issues? Physical problems with the HD, a virus, anything else?
What is my best bet for avoiding a situation like this in the future? RAID setup, OS system backup with Ghost for example. I am looking for something cost effective and not incredibly difficult to setup.
It costs me much lost time and money to have my system down for a week at a time while I buy new parts so I would like to avoid this from happening a fourth time. While I am at it I will probably get a new mobo as well (p35 or p45) which I think will be much more stable for my setup. At one time I actually thought about doing sli but I don't think that will be happening.

I had just upgraded from a e4300 to the q6600 and installed 2 more gigs of RAM before this all happened. I don't think this caused the problem because it was working fine for a while afterwards but I should throw it out there in case I am overlooking something.

Any other thoughts are welcome. Thanks in advance

It's a faulty disk, something went wrong during production. Replace it.
How old is this system? Warranty?
You took ik back to the local store and they flagged the bad sectors. That's service! You will have problems with this hard disk for ever.
If you have lot's of personal files (like pictures) get an external disk for backing up. A hard disk should be free of problems for years.