Go to Spell with Flickr.

Type in the desired text for your banner and click "spell."

You may change the tile size to regular (larger) or square (smaller). The size you want will depend on how long your banner will be.

Copy the html code for the word.

Go to "Manage Wiki," then "Look and Feel," then "Themes and Colors."

Scroll to the bottom of the page and type in a name for your new theme. Select the theme to use as your base (Note: You MUST use the Flexfluid theme for this to work!). Click "Edit."

Scroll towards the bottom (or search) for:
<$WikiLogoOrSpaceName$>

Replace with:
<img src="html code here">
You will need to paste the html code from the Spell with Flickr site.

Click "Save." You will be taken back to the Theme page, and you will have to click on your new theme and click "Apply."