Hi MEC,
If you were creating your listings by typing them directly into the description editor, instead of by copying and pasting, you would be able to accomplish this by starting with an item details profile that has one line of text in the description editor that reflects the desired font and size. If that were the case, when you highlight that text with your cursor and type over it, the font and size specification from that existing line of text would be continued.
Since you are creating your descriptions in Word and copying them into the Auctiva description, however, this won't be a possibility. When you do this, the font and size specification that is used in your Word document will overwrite anything that is already in the description editor when you paste it into the editor.
If you have any additional questions or concerns, please feel free to contact our customer support team using the web form on the following page of our site: http://www.auctiva.com/help/requesthelp.aspx
-Mike