Windows 7: Licensing confusion, reinstalling Win 7

Please excuse my laziness in posting a question that most likely has been answered before, but I am exhausted from searching and reading conflicting, poorly explained articles and wanted to get a straight answer from the place where the best answers come from...forums..
I have two questions and will do my best to keep them short and concise. First, I purchased an OEM copy of windows 7 to put on a new build and everything is working great. My confusion is if down the line I need to rebuild that system that requires a new install of the OS. Can I reuse the Key for that rebuild?

Secondly, I have a laptop that is running Vista that I can't stand dealing with anymore and want to install Win 7. I want to do a clean install and don't know if I should purchase another OEM copy -better price then retail and I don't care about tech support- or go for the upgrade. I assume ether way I go the both come with the 32- or 64-bit version, I have not decided which I want to install. I should mention that I do not have any Vista disks, none came with the laptop when I bought it.
Thanks

Re the first question: You cannot legally reuse the OEM key if you move to a new motherboard. I have heard of some cases where MS will allow you to replace a motherboard if the replacement is the same model or if the same model is no longer available. It can depend on the mercy of the person you happen to get on the phone at MS. The general advice is to use a retail license if you are a regular upgrader.

Re the second question: you could go with OEM or retail. You could do a clean install or an upgrade install. Most would tell you to do a clean install. On a laptop, there might be more incentive to stay with OEM because you are less likely to put a new motherboard into a laptop. Most would also tell you to go with 64-bit if your hardware will support it and if you have at least 4 gb of RAM.

1. Yes - provided that you do not install a new mobo.

2. What is your question? But an OEM version would work.

1). Like others said, if you don't change the hardware you can reinstall that OEM copy over and over again.

2). You need another key for the second machine. It can be either OEM or Retail. So, you can save money with OEM and lose ability to move to another machine later, or pay for retail and have the piece of mind knowing that you can reuse it later on another machine and get support from MS.

You can change any hardware except the mobo and reinstall OEM as often as you want.

You want Upgrade version from Vista. OEM is for System Builders.

The System Builder (generic OEM) comes with an installation DVD for just one version: 32 bit or 64 bit. I've read that the key works with either version, but you'd have to come up with an installation disk for the one that you didn't buy. As far as I know, there'd be nothing about that to violate the EULA (end user license agreement). Using a System Builder license is already a violation of the license (it's intended solely for resale), but there appears to be no enforcement of that.