harddrive damaged? save files... replace harddrive?

Hello,

my son put a pretty strong magnet on my MacBook Pro, 2,2 Ghz Intel Processor, 15". I bought this MacBook around 2 years ago.

The MacBook froze and did not load again. The following error code was found by a technician who seemed to have done some tests: 4SNS/1/40000000. And I was told that this may have something to do with overheating.

But today another techician was able to get into the Install system Screen (Alt / ON)

and said that the processor or other hardware periphery is not damaged, and the harddrive is still working... but not completely... since we tried to access the files by connecting the computer via firewire to another computer and the files could not be accessed. Apparently the hiearchy can be seen but the files are not accessible. And I was told that perhaps some of the system files were probably damaged and that is why the system broke down...

I am planning to install another harddrive and save the other until I am able to maybe recover the files with a harddisk recovery program.

Can anyone recommend me a good affordable program to do this ?

And can anyone give me any other tips in this frustrating hour...?

regards,

Nadia