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#400
Well besides those references there are a few other things you can try. Since one article pointed to an item with the registry preventing the SP1 install that could be taken care of the next time you need a fresh install of Windows. Slipstream Windows 7 SP1 into a Installation DVD or ISO File
Besides a clean install however the link on the error screen is what to pay attention since the MS page will have precise instructions which saw immediate results when not having been able to get SP1 installed here.
The only thing that may run slow will be the installation of the service pack itself. Once on you shouldn't actually notice anything different.
As far as the need for any SP watch the last versions to now see SP3-XP or SP2-Vista required! Eventually SP1 for 7 and later SP2 will also become a requirement for various things.