Don't get the OEM version if you intend to switch back and forth.
The OEM version is meant to be installed on a "new" computer only. Our Macs don't technically qualify because we already bought them before we install Windows. OEM will install but MS doesn't approve and will happily revoke your activation and ability to use the product (without a refund) if they feel that you're violating the EULA or especially if the think you're trying multiple installs.
MS intends the OEM version to be "Married" to one particular computer as determined by unique hardware identifiers. They will interpret frequent changes in perceived hardware (even if it's running on the same physical machine) as an attempt to install on multiple computers.
Using Windows in a virtual machine like Parallels appears differently to the Activation Scheme than Boot Camp does.
The best fix is to crack the Activation, but that's illegal.
The Full Retail version allows you to remove from one computer and install on another. This would probably result in less of a hassle from MS.
I would call MS and explain to them exactly what you want to do before you buy Windows.
Probably they would like you to buy TWO copies of Windows, but maybe the Full Retail version permits this.
All of this nonsense is a big part of the reason that I switched to Mac.
Have Fun,
Keri[/QUOTE
I bought the full retail Windows 7 Home Premium (£102 in a well known giant supermarket, UK) not the OEM and installed on a Boot Camp partition iMac (late 2007, 2.4Ghz, 4GB RAM) and activated it. When I then switched to Mac and set a virtual machine up using Boot Camp, there were Prallels warnings that I would have to reactivate this (and Office MS) as there were significant changes to the machine Windows was on!
I then called a Customer Service Representative on the activation helpline and explained what I was using the software for and they said that was okay as it was really one machine and they helped me activate it on the VM using the sets of numbers etc.
So after a few hours, going between the two I seem to have full activation. The otehr great thing is anything I do on the VM is actually happening on the Boot Camp partition so it is genuinely just using the one machine.
Hope that helps?
Bill