I'm astronished and disappointed that Toshiba didn't ship laptops these with SD card reader drivers.
Well… all the drivers for Win XP for this series Libretto U100 are available on Toshiba European driver page…
So I’m wondering why you are disappointed about Toshiba…
However, I could find the driver choosing:
Product Type: Archive
Product series: Libretto U100
Short num: PLU10E
OS: Windows XP
Now you should get all the Win XP drivers.
I assume the Cardbus driver is the driver you are looking for… its should get the card reader controller to work.
Furthermore you should install the SD Secure Module. This software is an update for your TOSHIBA Secure Digital-Host controller.