The Floating block module allows you to keep html blocks, selected using jquery selectors in a fixed position on the page as you scroll. It works in a similar way the table header fixer in Drupal Core. This means that when the user scrolls their browser selected parts of the page can stay in the users view.
This is extremely useful when you have pages with lots of content and you want a side menu to stay in view.
Tips for using jQuery selectors
Using the default Garland theme in Drupal 6 example selectors would be:
#sidebar-left Float the left sidebar
.primary-links Float the primary menu
.block-user Float the user login block
The important thing is to look at the html drupal is generating for your page and look at the id or class of the element your want to float. Find out more about jQuery selectors... Additionally another very useful tool (if you are using Firefox) is Firebug.
If you have an issue with no being able to make an element of your design float please tell me which theme you are using, provide a link to your site or upload the html from a page on your site.