How many times can I do a System Reformat (non OEM)

I'm getting sick and tired of my Dell. I want to build my own next time (probably in January next year I'll upgrade. This computer is already 1 year old, as of June 2011). Just wondering, how many times can I do a system reformat (if any) on a custom build computer (non OEM)?

Thanks.

One number I heard is 2 per 90 days but you can always call Microsoft if it gives you an error when you try to do it more.

Another option is a tool to back up your tokens and then supposedly you just reapply them.

Won't help your custom built but for anyone finding this: Laptops are usually preactivated so, I believe, even after a reinstall you don't need to go online or call (someone correct me if they know different). There are also KMS keys that corporations use to activate many computers which also would not be subject to directly contacting Microsoft.

Thanks TM. I think it's that also. 2 per 90 days is more than enough, I'd do one ever 1 year - 6 months. Thanks a bunch.