Do you still have the orginal Grey CDs that came with your system or have a retail version of Mac OS-X? If not do you have a bootable external drive you can use or have a second Mac which you can connect your MacBook to using Target Disk Mode?
You do have a small issue here as you can't use the newer MacOS versions on your system natively (Snow Leopard OS-X 10.6.8 is as high as you can go). But, you can access your systems drive via Target Disk Mode with any Mac running the newer OS's as it will be acting as a external drive to your other Mac. The only caviot here is you need to have a common interface to connect the two systems ideally FireWire Vs USB.