A lot of people use ant all to build their Elastic Path projects. This is convenient when you're setting up your development environment because it builds the webapps and CM client binaries, and creates projects to import into Eclipse. On the downside, it can take a long time to do all that. As Tom pointed out in a recent blog post ( http://grep.elasticpath.com/community/techblog/blog/2009/01/27/ep-61-development-environment-tips-tricks), you really don't want to run ant all all the time. It's easier and faster to build your projects individually from within Eclipse.
Each webapp project (com.elasticpath.sf, com.elasticpath.cm, and com.elasticpath.search) has its own build.xml file in the root of the project directory.
If you only need to build one webapp, right-click the build.xml file in Eclipse's Project Explorer and choose Run As->Ant Build... . Then select the target(s) you want to run.
For more information on available ant targets, see the Elastic Path 6.1 Developer Guide (http://docs.elasticpath.com/display/EP61DEV/2+-+Using+the+Elastic+Path+Ant+tasks).