Dual-core pentiums are quite old technology now (discontinued in 2009) and most people would probably regard them as being at the low end of the spectrum for running either Windows 8 or Office 2013. No amount of upgrading the basic machine is going to turn it into something that will match a recent PC's performance; I doubt you could buy anything so lowly-spec'd for running Windows today. That said, you really don't need more than 4Gb RAM to run Windows 8 & Office 2013 -and you'll often find even entry level PCs with more than that.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]