I'd personally get a copy of a partition manager like Partition Magic. I'd then resize your existing partitions so as you can create a partition specifically for LFS.
My current setup looks like this:
Part. 1: Windows XP
Part. 2: Gentoo Linux
Part. 3: LFS
Part. 4: Swap Space for whichever Linux distro is booted.
(if you don't want to or can't create another partition then there's a hint on http://hints.linuxfromscratch.org
that describes how you can install LFS on the same partition as your existing distro. Once you've got your partitions sorted you'll need to boot into your SUSE system. From here you can issue all the commands given in the LFS book. Once you've got your LFS system up and running then you can go into your partition manager software again and remove the SUSE partition if you really must - note that you'll have to play around with your boot loader config, fstab files, and possibly more in order to properly boot LFS again.
Hope this gets you started,