To downgrade to XP from Vista on a Toshiba L305-S5921 Intel based laptop, you first must go into the BIOS on boot and change the SATA drive from AHCI to Contemporary. The XP install disks will then load XP and install.

Unfortunately, you will need to download and install several drivers to fix hardware issues. The files you will need are:

Audio Device        driver-audio-Realtek-28284A
Ethernet                driver-LAN-realtek-27410A
Ethernet                driver-wifi-Atheros-27763A
Modem Device     driver-modem-26470A
SM Bus                driver-chipset-intel-27611B
Video Controller    driver-video-intel-28283

These are available on the Toshiba web site.

After downloading and installing, reboot to make sure all drivers are completely installed. Then go to Start-Control Panel-System-Hardware-Device Manager to see if all the drivers are installed properly. If not, you will find a yellow mark on the driver not working.

Once installed, the XP should boot and operate normally.

Update:  6/24/2009
Unfortunately, the XP I installed would not activate with Windows activation. After much investigation, I came to no conclusion as to why it would not activate, so I reinstalled Vista. If you have activation problems, please let me know so I can post a note about it. It might be a Toshiba problem.

Calling Microsoft is like calling the police to report yourself. It doesn't matter if you have done no wrong, if the police show up. So I am scared to call them to try to diagnose if some one else had actually used that license I purchased, unwrapped and supposedly unused.

Miranda decision: anything you do or say to anyone working for the government (or Microsoft) can and will be used against you in a court of law. To avoid self incrimination, use Linux: Linux seems to work better anyway.