You may need a special bootdisk or dirver for
SATA. It is fairly new technology:
sata.i: Serial ATA support bootdisk for
Slackware 9.0.
This bootdisk is based on linux-2.4.21-pre7 with support for
Silicon Image SII3112
SATA controllers. After installing with
this bootdisk, you will probably need to download the kernel
source from ftp.kernel.org
and compile new kernel modules (or
build the drivers you need into a new kernel).
There is a thread on this topic already:
http://linuxquestions.org/questions/history/134759
It seems
Slackware is not up to speed on
SATA...