I know that Slackware 10.0 install disk recognises USB harddisk!
Infact this is how I backup data from crippled Operating Systems.
I am not sure whether it is supported by the default kernel of Slackware 9.0
But there is no harm trying.
1. Boot-up Slackware 9.0 Install Disk 1
2. do the necessary (login)
3. fdisk /dev/sda
IF you get the normal fdisk menu, then just go ahead and partition it as you wish. Commit the partition and start installation (setup)
IF you get some error message saying that device do not exist, THEN you have some hacking to do.
What you need is A bootdisk which supports USB Mass Storage kernel and the rest of your hardware on your lappy.
To do this, please search the forum on how to create the bootdisk. You will also need 2 other disks, install.1 and isntall.2 this can be obtain from the rootdisks folder in your CD.
My advise is, just go for Slackware 10.0
You can just use bare.i from Slackware 10.0 since it supports USB mass storage.