my.build.properties
build.properties

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:
<property file="my.build.properties"/>
<property file="build.properties"/>
<property file="${user.home}/build.properties"/>

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.