Assuming you don't want anyone recovering the data?
I don't think there's a fool proof way to completely erase all data without making it nonrecoverable, the best thing to do would be to format the drive a few times, and then write zeros to the disk.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w