, if I understand you correctly, you have a machine with a) only one primary partition, and on that partition you have Windows; b) you attempted to install SL in the remaining HDD space and let the SL Installer partition that space.
If you can boot Windows, or use another machine, download the SystemRescueCd
ISO and burn a LiveCD or Live pen drive for SystemRescueCd. Then boot that and use GParted to wipe the Linux partitions on your HDD and create the following three fresh partitions. As you only have one primary partition, you can create three more primary partitions, as you can have up to four primary partitions on a HDD.swap
(Linux swap file system) primary partition. Make this the same size as your RAM if you have plenty of HDD space and you want SL to be able to hibernate. Otherwise, a minimum of 512 MB is sufficient./
(ext4 file system) primary partition. Make this 32 GB (or more, if you have plenty of space)./home
(ext4 file system) primary partition. Fill the rest of your HDD's free space with this. All your personal documents, music and video files will go on here later.
Now shut down, load the SL LiveDVD or Live pen drive, boot your machine and run the Installer. When you get to the screen that asks you what type of installation you would like, select Create Custom Layout. Then manually select your pre-created partitions (you can re-format them as ext4) and proceed from there. Don't let Sabayon create the partitions for you, and don't use LVM. See how you get on doing it that way.