How can I make sure my computer is completely "empty" before I sell it?

DO you want to sell it with an OS?
If not
a) open it up (Its not a mac is it?) and remove the HD
b) plug the HD into an external HD reader and format it using another computer (this will completely wipe the HD of everything!
c)put it back together

if you want to sell it with an OS
just put the windows install CD in the drive and re-install windows choosing to wipe re-format your HD when the option comes up.

Its a Mac. Sorry I didn’t specify.

if it’s a mac, my advice, pop in the install disk, go to disc utility, erase, security options, and then overwrite it with 0’s, 3 passes should be enough, you can go up to 64 if i’m not mistaken

What iwamoto said. Just make sure you boot from the CD/DVD when you use Disk Utility.

i thought that would come naturally, can’t erase the drive you use right ?

Just trying to remove any possible confusion.

i know, actually i thank you for it, i tend to take things too…obvious

Thanx!

If you’re REALLY serious throw the HDD away. Someone with the right resources could extract data from a formatted drive.

even if you overwrite it with 0’s 64 times? has to be an extremely clever and desperate man, haha