man shred
grep for ext3 with -j flag. shred cant delete files used in journalled filesystem, thats rule number 1. there is another option secure delete look for it in thc (the hackers choice) else use wipe, but let me warn you, you may grab yourself a flask of beverage and see it vanishing slowly like camphor.
mkfs.ext3 -jv /dev/hdX and shred? hehehe wont work! the -j flag will restore it. secure delete or wipe even if you use shred -n 25 -v -z -u file or device. if device and mounted off then only. else? experiment and share and tell us what not to do!