OEM vs Full Product

Hopefully this is the right area...

What is the difference between OEM and Full Versions of software, in this case Windows XP Pro.

I know the basics that you get the CD with the EULA and proudct key with no manuals but I am looking for a bit more details.

1) Can this be installed on ANY PC regardless of it's make/model/etc. The reason I ask is I have a Dell Win2K CD that when I tried to boot from a non-Dell PC it would not let me.

2) Do you HAVE to do a full/fresh install of the OS (or any package) if you get this version?

3) Any reason NOT to buy OEM, seeing the cost is 100% better and you still get the same product.

Full retail comes in a pretty box, has more warranty (or in the case of software, free support) and costs more.

OEM comes barely packaged, has less or no warranty from the manufacturer (no free support for software) and costs less.

Clear as mud?

The extra you pay for the retail goes towards product support for the most part and partly for the pretty box you get.

Yeah, Microsoft has changed it's OEM licensing a bit. OEM copies can only technically be installed on one computer and that OEM copy must be sold with that computer if the computer is re-sold. Also, if you upgrade a PC with an OEM copy of Windows, you may have to purchase another OEM copy. With a retail copy, you're allowed to transfer that copy to a new PC when you purchase one... but it still must be removed from the old PC before it's sold.

There are exceptions made for defective equipment of course... but does MS really have to know if you're upgrading or simply replacing dead parts?