I would have to disagree with higher cpu frequency is better, unless you are comparing the same amount of cores. Remember, Microsoft Excel and Acess take full advantage of multiple cores, so an Intel P4 at 3.0Ghz would not be better than a AMD Athlon II X4 620 at 2.6Ghz.
For Microsoft applications, I would go with a slower multiple core cpu over a higher frequency cpu with less cores.
More RAM will help with excel the most if you on a spreed sheet with some serious amount of pages more RAM will make it quicker going between pages but most computers these days are coming with 4 gigs atleast so that shouldn't be an issue on a newer computer. If your on an older computer that only has 512MB or a 1GB more RAM will definitely help on larger spreadsheets.