iXBT Labs posted a guide about choosing an office PC
>> Choosing an Office PC
Unlike gaming PCs, office configurations are chosen with the help of universal benchmarks. In practice, the most adequate tests for office hardware these days are SYSMark 2007 and PCMark Vantage. We compiled the results obtained in these benchmarks with different processors, graphics cards, and memory sizes. Traditionally, there's an interactive configuration calculator for your convenience.
>> Choosing an Office PC