The wolips.properties file tells WOLips (and the Ant based build) where to find the various parts of WebObjects and friends. This replaces the wobuild.properties files used by earlier version (pre-New Hotness) of WOLips.
The location of this file differs by operating system:
C:\Documents and Settings\<user>\Library\Application Support\WOLips\wolips.properties
The wolips.properties file should be created automatically, but if this does not happen, it can be created manually (e.g. with a text editor). Example contents of this file (modify to match the locations on your machine):
Example on Windows:
See Using WOLips With Multiple Versions of WebObjects for how to use different wolips.properties files with different WO version.