HAH! I figured out how to interface with their saverbeans API on Windows XP.
I got the bouncingline screensaver to work. Here are
complete instructions (only tested with bouncingline) on how to build an
example:

Download 'ant' and set all the environment variables as specified in the
installation documentation.

Download the latest Saverbeans SDK from:
https://jdic.dev.java.net/servlets/ProjectDocumentList?folderID=1330&expandFolder=1330&folderID=1330

Extract the SDK to a directory that doesn't contain spaces or any special
characters. Preferably "C:\saverbeans".

Download any screensaver example from java.net. The bouncingline example is
included inside of the SDK download inside of a .zip file.
Other examples are available on CVS from:
https://screensavers.dev.java.net/source/browse/screensavers/src/#dirlist

From the root directory of the screensaver source download, copy
"build.properties.sample" to "build.properties". Edit this file so that
saverbeans.path is set to "C:\saverbeans", or wherever the Saverbeans SDK
ANT+API jar files are located.

Open a console window in that directory. Enter "ant dist". You will probably
get a "taskdef" error. To resolve this, edit the build.xml file and replace
any occurances of "${saverbeans.path}/" with "c:\saverbeans\", and then 
enter in "ant dist" again.

Inside of the newly created directory "dist", copy all files inside of the
"win32" subfolder, except for the "README.TXT" file, into your Windows XP
System directory (ie: "c:\windows\system32").

You should now be able to run your screensaver like you would any standard
screensaver.