Welcome to OSNN.
Toshiba does not support upgrading from VISTA to XP. PERIOD! If you do so you are on your own.
I recently purchased a Toshiba and have fully researched and made the transition.
Dell and Compaq do support the changeover and are prefered for this reason. If you can, I recommned a return and change of brand.
Correction on 10-31 coutesy of:
@LeeJend - Dell does not support down grading from Vista to XP. I called them and asked about it for my PC. They told me that if I do downgrade I loose all warantee and the like with it. They recommended me to stay with vista till my warantee runs out. By which point they "Should" have Vista SP1 out.
Looks like the only Dell option is to buy it with XP.
If you are stuck with the Toshiba I have fairly successfully worked through the process and can help. To retain your hardware warantee (forget about Toshiba support, if you do this you are on your own) you want to setup your PC as a dual boot system where XP has 50-80% of the harddisk assigned and VISTA and the Toshiba recovery center get the rest.
First you need a legit copy of XP with activation possible.
Next you need to go through device manager on VISTA and identify all of your hardware devices and the manufacturer and version (CPU, chipset, wifi, lan, audio, HD, DVD, etc.)
Third you need to scrounge (and this is scrounging, Toshiba will hide what you need) all of the drivers for XP for the devices identified.
http://downloadcenter.intel.com/Product_Filter.aspx?ProductID=757&lang=eng
possibly
http://www.atheros.com/news/linux.html for wireless
possibly
www.realtek.com for audio
possibly AMD if you have one of the rare AMD based laptops
You will find some of what you need on the Toshiba site listed for other laptop models. It depends on the chipsets your laptop uses. European and Canadian Toshiba websites are more use full than the USA sites. A major problem will be if you got your laptop at a USA computer retailer Each of these is uniquely configured for the retailer and finding equivalent models is nto trivial.
http://209.167.114.38/support/download/ln_byModel.asp
This site has a good tutorial and link to a tool you will need to setup the VISTA dual boot system more easily.
http://apcmag.com/5485/dualbooting_vista_and_xp
The 6 month long thread I used to help scrounge what I needed. You need to skim through the whole thing and look for models/issues similar to what you run into:
http://discussions.hardwarecentral.com/showthread.php?t=175186&page=3
I was successful in setting up XP to about 95% and I have a great laptop that I got dirt cheap and runs well with XP. With VISTA it is a useless slug devouring resources. I did have to install after (free) market products for power regulation to reduce screen brightness and throttling CPU speed to keep the battery charge life you get under VISTA.
WARNING - When re-partitioning your HD to add XP do not wipe out the Toshiba system recovery partition or delete the VISTA install partition! You can use the system recovery partition or the recovery CDs provided by Toshiba if the dual boot set up goes bad and you need to start over.
Repost or PM me if you need help getting the power management working. I used GAPA for manual brightness control and Winthrottle for automatic CPU control. Roghtmakr is the recommended PCU control utility but it wouldnot work on my laptop/chipset.
If you want to try and improve VISTA I got substantial improvements (it still sucks compared to XP) by:
Adding 1 gig ram for 1.5 gig total.
Remove the junk, resource hog macafee AV suite and install AVS (free) or another (not NORTON).
Anything else you don't NEED remove from the HD and/or start up menu.
As for VISTA being good? Any new OS that requires me to throw away more paid for $oftware investment than the purchase price of the new PC is junk! It has a few nice features and some immensely annoying ones. In a year or two and if MS provides free upgrades to all my other software VISTA may be worth using. Of couse it is still a resource hog that turns a perfectly good PC into a dog.