By default the descriptions of your map items are in plain text. However, you can use rich text or HTML. To do this:
Create or open a map.
Click the appropriate placemark, line, shape. The info window appears.
Click Edit.
Choose Plain Text, Rich Text or Edit HTML.
To edit rich text descriptions, select the text and use the icons above the description field:
To use HTML descriptions, add HTML in the description field. Some HTML may be stripped from the description if it is considered unsafe or malicious.
Click OK to save your changes.
http://maps.google.com/help/maps/mymaps/create.html
Use Google Maps to:
** Draw lines and shapes to highlight paths and areas**
** Add your own text, photos, and videos**
http://maps.google.com/support/bin/static.py?page=guide.cs&guide=21670&topic=21676&answer=144364#text
Adding Rich Text or HTML Descriptions
By default the descriptions of your map items are in plain text. However, you can use rich text or HTML. To do this:
Create or open a map.
Click the appropriate placemark, line, shape. The info window appears.
Click Edit.
Choose Plain Text, Rich Text or Edit HTML.
To edit rich text descriptions, select the text and use the icons above the description field:
To use HTML descriptions, add HTML in the description field. Some HTML may be stripped from the description if it is considered unsafe or malicious.
Click OK to save your changes.
http://www.youtube.com/watch?v=TftFnot5uXw&feature=player_embedded#!