Will scratching the internal disks with a screwdriver be enough to render them completely unreadable? Do I risk coming into contact with dangerous materials myself?

Anyways, Thanks for the help guys. Much appreciated. :)

- Erase the drive securely.
- Leave the drive in working condition.

Pick one of these; you cannot have both. If the data is truly sensitive then your only legal and ethical recourse is to destroy the drive, because as long as the drive is intact your data CAN be recovered. You might be able to make someone's life very miserable as they try to recover the data -maybe even to the point that they give up before succeeding- but you cannot make it truly irrevocable.

The NSA recommends melting the drive with thermite, breaking the resulting lump of metal into little pieces, and burying the pieces in separate locations. You don't necessarily have to go THAT far; smashing the drive with a sledgehammer is likely enough to deter anything short of an intelligence agency. But the bottom line is that destroying data involves actual destruction.

I don't think scratching them will be enough, you'll need to make sure you do something capable of cracking or breaking the disc in general.  Since the internal discs don't work like a CD/DVD, HDD discs are dependant on magnetic fields, so a scratch will not affect the data.  A crack or break in the disc causes major problems because is will create discontinuities in the magenetic fields, making them completely unreadable.

On older HDD drives there is a possibility to come into contact with lead, mercury (which should be highly unlikely from a drive made in the 90's) and there are some potentially other harmful materials that are used a fire retardant materials (mainly PBB's and PBDE's).  I wouldn't be too worried about any other harmful materials.  The ones that would most likely be there are only heavy metals, so you should just make sure you wash your hands well before eating/smoking/etc.

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