I use a system of two properties files:
my.build.properties takes precedence over build.properties, allowing team members to override properties with machine specific values. This is where you'd put your absolute paths, such as the location of Tomcat/WebLogic/etc.
Towards the top of the Ant script, include:
Also be sure to include my.build.properties in your .cvsignore file so team members don't accidentally check in the file and overwrite your own properties.