Each developer or user has the right (or is forced by administrators) to put resource such as jar files and libraries in different locations
Try to avoid having ANY local file system location dependencies in your build files. Make sure you NEVER put C: in a build file. This is just plain bad behavior
Separate local file system access points in an external "property file"
Warning: property files are read by Java tools and are not always path separator aware. You can use "\\" on java, or, knowing that Ant expands existing properties, ${path.separator}
Allow people to check out all the files in a project including the build.xml file, customize their local library paths and build
Third party projects such as Ivy and Maven2 Ant tasks try to automate the entire library management process. Consider these on a very large/complex project.