Is the hard drive a SATA drive? Windows XP doesn't have native support for SATA drives. You need to press F6 when you boot from the CD and then provide the SATA drivers from a floppy.
To find those, you have to know the make of the SATA controller on your laptop (it's sometimes integrated with the motherboard). You may have to look it up in the manual. If you don't have the manual, you can probably download it from the Toshiba web site by looking for your specific model. I see a bunch of different A205's, so you'd have to look for the specific one for your model.
http://www.csd.toshiba.com/cgi-bin/t..._sc_modSel.jsp
Download the manual and see what kind of motherboard chipset it uses. Then you may have to go on the manufacturer's web site (unless it's already on the Toshiba site) to find the drivers. If you need help, get back to us (be sure to give us the exact Toshiba model number)
Other things to take into consideration:
If you don't have a floppy drive, you may need to use an external USB one.
If none of the above works, try going into your BIOS (at startup, it may tell you to press a key like F10 and Del or something else to get into setup), and look around the menus. Sometimes there's a setting that allows the SATA controller to act like an ATA one. It may be named something like "legacy IDE" or "AHCI". If you set that, Windows XP will detect the drives since they start acting like old PATA drives again.
Also note that downgrading to XP involves hunting down for drivers for your devices (you'll likely see a lot of yellow exclamation marks in device manager on the first run). Some of the driver installation programs for Vista available for download on the Toshiba site may also have bundled drivers for XP, so you can try them first. If you need help in that department, get back to us.