Most of your questions have been answered in recent threads.

You'll still need to phone MS on occasion if you're swapping a lot of hardware or transfering.
I will do my best to answer your questions, but to be honest some of the licensing is difficult to obtain unless you have a copy of the OS on hand. If I am wrong on any of this I hope someone will correct me.
http://download.microsoft.com/documents...6c019b-fa71-4fc9-a51d-a0621bddb153.pdf
- All OEM - not transferrable (never has been)
- OEM upgrade - According to the OEM EULA you cannot transfer it, and installing the upgrade revokes your old license and you may not reuse it.
- Anytime Upgrades - 1 transfer if you're upgrading a non-OEM copy
- Retail upgrade - still searching.....
- All Retail full versions - unlimited transfers
If you have OEM and upgrade your motherboard you are violating the EULA and engaging in casual piracy.
http://oem.microsoft.com/script/contentpage.aspx?PageID=552846#faq1
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Vista is identical to XP in regards to OEM licensing.
Q. Can a PC with OEM Windows XP have its motherboard upgraded and keep the same license? What if it was replaced because it was defective?
A. Generally, you may upgrade or replace all of the hardware components on your customer's computer and the end user may maintain the license for the original Microsoft OEM operating system software, with the exception of an upgrade or replacement of the motherboard. An upgrade of the motherboard is considered to result in a "new personal computer" to which Microsoft OEM operating system software cannot be transferred from another computer. If the motherboard is upgraded or replaced for reasons other than a defect, then a new computer has been created and the license of new operating system software is required. If the motherboard is replaced because it is defective, you do NOT need to acquire a new operating system license for the PC as long as the replacement motherboard is the same make/model or the same manufacturer's replacement/equivalent, as defined by the manufacturer's warranty.
The reason for this licensing rule primarily relates to the end-user license agreement (EULA) and the support of the software covered by that EULA. The EULA is a set of usage rights granted to the end-user by the PC manufacturer and relates only to rights for that software as installed on for that particular PC. The System Builder is required to support the software on that original PC. Understanding that end users, over time, upgrade their PC with different components, Microsoft needed to have one base component "left standing" that would still define that original PC. Since the motherboard contains the CPU and is the "heart and soul" of the PC, when the motherboard is replaced (for reasons other than defect) a new PC is essentially created. The original System Builder, therefore, can not be expected to support this new PC that they in effect, did not manufacture.
Here are all of the
Vista OEM EULA's that I pulled from my OEM copy of Home Premium. Here's most of the pertinent infomation.
If you comply with these license terms, you have the rights below for each license you acquire.
1.
OVERVIEW.
- a. Software. The software includes desktop operating system software. This software does not include Windows Live services. Windows Live is a service available from Microsoft under a separate agreement.
b. License Model. The software is licensed on a per copy per device basis.
c. Edition Specific Rights. See the Additional License Terms sections at the end of this agreement for license terms that apply to specific editions of the software.
2.
INSTALLATION AND USE RIGHTS. The software license is permanently assigned to the device with which you acquired the software. That device is the ?licensed device.? A hardware partition is considered to be a separate device.
- a. Licensed Device. You may install one copy of the software on the licensed device. You may use the software on up to two processors on that device at one time. You may not use the software on any other device.
b. Number of Users. Except as provided in the Device Connections (all editions), Remote Access Technologies (Home Basic and Home Premium editions) and Other Access Technologies (Ultimate edition) sections below, only one user may use the software at a time.
c. Alternative Versions. The software may include more than one version, such as 32-bit and 64-bit. You may use only one version at one time. If manufacturer or installer provides you with a one-time selection between language versions, you may use only the one language version you select.
13.
UPGRADES. To use upgrade software, you must first be licensed for the software that is eligible for the upgrade. Upon upgrade, this agreement takes the place of the agreement for the software you upgraded from. After you upgrade, you may no longer use the software you upgraded from, except as permitted in the Downgrade section below.
14.
DOWNGRADE. Instead of using the software, you may use one of the following earlier versions:
- ? Microsoft Windows XP Professional,
? Microsoft Windows Professional x64 Edition, or
? Microsoft Windows XP Tablet PC Edition.
This agreement applies to your use of the earlier versions. If the earlier version includes different components, any terms for those components in the agreement that comes with the earlier version apply to your use of them. Neither the manufacturer or installer, nor Microsoft is obligated to supply earlier versions to you. You must obtain the earlier version separately. At any time, you may replace an earlier version with this version of the software.
15.
TRANSFER TO A THIRD PARTY. You may transfer the software directly to a third party only with the licensed device. You may not keep any copies of the software or any earlier version. Before any permitted transfer, the other party must agree that this agreement applies to the transfer and use of the software. The transfer must include the Certificate of Authenticity label.