If you're referring to an art border, BorderArt is available only for page
borders. If you're referring to a clip art border, you would find it in
Insert | Picture | Clip Art. Searching for "Christmas border" seems to give
the best results for me (and you may need to search online).
Not where its easy to find, but logical when you eventually find it! In the
Paragraph section on the Home Tab, the lower right hand tool is for adding
borders. Click on the right arrow, select Borders and Shading and then
select the Page Border Tab. Note that an additional drop down selection box
appears in the lower centre column labeled ART.