Always choose an administation theme.

You do this by going to:

Administer>Site Configuration>Administrative Theme

Choose a standard out-of-the-box theme such as Bluemarine or  Garland.

Why? Well if you are experimenting  with doing your own theme and something goes wrong, the site can go blnk and there's no way to get back into it!

Using a reliable Admin theme gets rid of this problem.