In the top-left corner of the document pane you should see a small right-angled bracket that looks like an 'L'. That's for setting a left-aligned tab-stop. If you click on that twice it will display a backwards right-angled bracket, for a right-aligned tab-stop. To use it simply click in the cell, then click on the ruler at the position where you want the stop to go. If you can't get it exactly where you want it, you can drag it left or right to re-position it; otherwise you can use Home>Paragraph>Tabs to input the exact position you want for it (make sure to choose the appropriate options).

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]