Drupal 5.7 comes with 6 basic themes. The one we have been seeing is the 'garland' theme.

Go to your website.

Login username 'eve', password.

Select > Administer > Site building > Themes.

Select > Administer > Site building > Themes > [scroll down] > [Default,change to] pushbutton > Save configuration > Log out.

Notice our block 'Our Company/ About Us/...etc..' did not display above.

Login username 'eve', password.

Select > Administer > Site building > Blocks > [Our Company] > [Region] left sidebar > Save blocks > Log out.

Note: The power of Drupal allows us to create and bind themes with different content topics. Example, say we create more blocks with different content topics eg. accounting, agriculture, manufacturing, health and 'bind' different blocks with different themes.
If you're demonstrating your website to say an accountant, just show him that theme say, chameleon that's displays the block containing accounting topics.