Using Joomla My Site, is there a way to add new templates or edit the old ones like beez or milky way?

The easiest is to use pre-made templates:

http://www.gavick.com
http://www.youjoomla.com
http://www.joomlart.com
http://www.joomla-themes.co.uk
http://www.joomlashack.com
http://www.joomla24.com
http://www.osskins.com
http://www.themesbase.com/?category=Joomla

Use the Joomla installer to install the new templates.

If you are handy with a graphics editing program, you can alter Beez and Milky Way, just make a copy of one of these default templates and add it. I did a demo with some free templates and a couple I edited on http://demo.kgraff.net/cms/ if you want to look around. I installed a "template changer" (from the Joomla.org site) so people can view the same content in different templates.

Give it a try! It isn't exactly rocket science, but fun.