I think when you buy the OEM version you have to choose which bit version you want.
With my machine 64 bit won't work. I only have 1 gig of ram now. And I only have 3 slots for a max of 3 gigs.

What is this OPK, OEM Preinstallation Kit?
http://oem.microsoft.com/script/contentpage.aspx?pageid=565701#features

Do I really need this or can I just install Windows 7 from the OEM disc and be done with it?

OK, after much searching I found the OPK is needed only to add Microsoft Office 2007 to the system. More info here:
https://partner.microsoft.com/UK/40047375?PS=95000124

Danny

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