Unsure about settings

[rbl]

Hi!
I've read the manual before and after I purchased SD a month ago, just finished another reading and I'm still unsure if I'm taking the right approach.

I have an external 160GB firewire drive from which I boot every now and then for maintenance operations, and it's also the repository of my larger files because my iBooks HD is only 30GB.

I want to use SD for daily backups of my user folder and an occasional backup of all files.

Seems weird to me but from what I could understand, for my first backup I need an empty destination disk no matter whatever settings I choose.
Is this so?

Thanks! =)
Ricardo