If the table you insert has borders by default, remove them with Ctrl+Alt+U
or by selecting the table and choosing None in the Borders and Shading
dialog or No Bordero on the Borders palette flyout.

Select the table and, on the Row tab of Table Properties, check the box for
"Specify height," then choose Exactly and type in the appropriate
measurement.

Do the same for preferred column width on the Columns tab. You'll need to
disable auto resizing by choosing Fixed Column Width on the Table | AutoFit
menu or clearing the "Automatically resize to fit contents" check box in
Table Properties | Table | Options.