I personally use PGP Wipe for situations like this. If we're going to talk about sufficently motivated people, any hack you write or tool you use should wipe multiple times. Once is not enough to ensure data unrecoverability, try 3 passes; or upwards of 9 passes if you're really paranoid...
- jbWare
Just because you're paranoid, doesn't mean they're not out to get you.