>>>I have run into this before, but haven't really researched it. I am horrible about keeping my Windows XP CD's and I usually keep them as ISO's and burn them to a CD when needed. Sometime a particular key doesn't work with a CD so I try the next CD and it works. Are there different versions or something? I don't think it is the OEM version. I have the regular key on the sticker on the side of the case and it says it's an invalid key.
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>>Yeah, from what I've encountered over the years there are different keys for:
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>>- full version vs. upgrade
>>- full packaged product vs. OEM (and probably vs MSDN, academic etc.)
>>- XP w/o SP (i.e. "SP0"), SP1 and SP2 (and the soon-to-be-released SP3)
>
>OEM license keys have OEM in them, don't they? This doesn't - it's a regular key. It's not an upgrade either. It's an IBM desktop and we bought it with XP installed on it, so maybe it IS an OEM license.
>
>We also bought it before SP2, so that can't be it.

It is almost certainly an OEM license if it came pre-installed on an IBM computer.

No, the "activation" key that's present on the sticker is a 5x5 character string just like any other. The registration key (more like a registration number, actually) does contain the string "OEM" for OEM installs - this alerts MS support that you don't qualify for free support when you call them. You can view your registration number on the General tab of My Computer...Properties.

The activation key and registration number are two different things.