Q#1. You have Vista installed on a hard drive, not the mobo. Windows will be specific to your mobo however...you more than likely won't be able to just plug your hard drive into your new mobo and fire it up. Windows will be mad at you because of the new chipset on your mobo and probably won't start. I followed this when I did it with XP but I am not sure if Vista is the same though. I would assume it is pretty close but do some more searching to confirm.
Q#2, I am pretty sure no but you can again, do the trick below as long as you use the hard drive. You can't just pop in the CD with a new system as far as I know.
Edit: I think I tried that way back in the day of my Dell usage and when autorun kicks in it tells you that it is not a Dell or not the correct PC or something to that order. As long as you keep your Hard drive with your Dell specific OS on it though, it will work with any mobo if you do the thing below.
Upgrade an existing motherboard
This scenario assumes that your existing motherboard works and that you can start the existing Windows installation on the hard disk.
To replace a working motherboard with an updated motherboard and to then reconfigure Windows to work with the new motherboard, follow these steps:
Start Windows, and then log on as an administrator.
Insert your Windows CD in the CD-ROM drive or the DVD-ROM drive, and then let Autorun start.
Do one of the following:
For Windows Server 2003:
Click Install Windows Server 2003.
In the Windows Setup window, click Upgrade (Recommended) in the Installation Type list, and then click Next.
Follow the instructions on the screen until the computer begins to restart.
For Windows XP:
Click Install Windows XP.
In the Windows Setup window, click Upgrade (Recommended) in the Installation Type list, and then click Next.
Follow the instructions on the screen until the computer begins to restart.
For Windows 2000:
Click Install Windows 2000.
In the Windows 2000 Setup window, click Upgrade to Windows 2000 (Recommended), and then click Next.
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Follow the instructions on the screen until the computer begins to restart.
Just as the computer begins to restart, turn off the computer.
Replace the existing motherboard with the new motherboard.
Turn on the computer, and then allow the upgrade to continue.
Setup installs the HAL, the IDE controller drivers, and any other drivers that the new motherboard must have.
After the upgrade is completed, reinstall any service packs or hotfixes that you had previously installed.