It looks like the .Extend and .Expand methods of the Selection object might do what you want. This is from the help for extend:
Code:
With Selection
' Collapse current selection to insertion point.
.Collapse
' Turn extend mode on.
.Extend
' Extend selection to word.
.Extend
' Extend selection to sentence.
.Extend
End With
Or try this:
Code:
Selection.Expand ' default unit is wdWord