Many websites provide access to forms in PDF format. Unfortunately, not all PDF forms are coded to allow the user to fill them in online. You have to print out the form and then fill in the blanks by hand (blecch) or with a typewriter (scarce as hen's teeth.)
The good news from folks at the Wisconsin State Law Library is there's a free PDF mark-up tool called PDF X-Change that lets you make PDF forms into "fillable" ones.
Update 9/16/10: Use this software if you're registering for the WLA Conference using the PDF of the registration form. Daryl at Fond du Lac Public Library wrote to say he downloaded the software to edit his WLA form; "It was easy to use and intuitive, and it will definitely come in handy."
The Wisconsin State Law Library has information on downloading & installing it in their Tech Tip column:
Once PDF X-Change is installed on your computer, you can use it to view and fill out any PDF form you've downloaded. Simply click on the Typewriter tool, then click back to the space you want to fill in and begin typing. When you're finished, you can save and/or print the form.
Source: Wisconsin State Law Library, WSLL @ Your Service September 2010