Installing Windows XP Pro on T400: Problems! Please HELP!

Hi there,
I bought a refurbished ThinkPad T400 from an ebay seller for a good price. The auction was supposed to include a Windows XP Pro key and CD. There's the first problem. As far as I can tell, there is no XP license included, just a Vista license key. After looking around a bit, I discovered that I should be able to downgrade my Vista license to XP, according to this website:
http://www-307.ibm.com/pc/support/s...estyle=lenovo&lndocid=VSTA-DWNGRD#downgrading

1. Has anyone tried this?
2. Does doing this invalidate your Vista license? In other words, if I decide to switch to Vista later, can I still do so (legally), by using the original Vista license key?
3. Do I have to order an XP install/recovery CD from Lenovo or can I just get the XP Pro license key somehow? (I don't want to spend another $NN bucks on ordering a CD I don't really need, when I really just need the key to activate Windows.)

Next, the auction actually included a Windows XP Pro OEM CD, but when I tried to install using this CD, I just get a blue screen (BSOD), citing error:
"Stop 0x0000007E"

I've read in various posts that this is a SATA error, and I just need to go into BIOS, change the SATA setting to compatability mode and everything should install. Well, I did that, and I got the same error again, repeatedly. The Windows XP install starts loading config files then crashes in a BSOD.

Can someone please help?!

 

What version of Vista did it come with? You can use nLite to slipstream the SATA drivers or service pack three into your installation disc, both of which have the necessary .dlls.

 

The auction included a Windows XP Pro OEM CD but a Vista Business license. Uhhh.

I'm not familiar with nLite or slipstreaming. Can you explain?

 

Download it. It's pretty easy. Post back if you get stuck.