Installtion from HD instead CD (boot disk image)

Hi,

I want to install Linux with GenToo and instead of burning a CD I rather
like to boot the live cd iso file from HD - like I was able to with the
(currently on my box installed) Mandrake distribution. So my question is,
where to get (or build) the approriate boot disk image?
I tried a Slackware bare image file but that needs a root disk - but before
more RTFM I wanted to have confirmation that this approach will be of any
luck, e.g. if there is some special "iso filesystem (?) driver" on the boot
disk needed for the usage with the mount command (that I would use to attach
the live cd iso).

Regards,
Thilo.