<target name="retrievePkg">
  <mkdir dir="retrieveUnpackaged"/>
  <sf:retrieve username="${sf.username}" password="${sf.password}" sessionId="${sf.sessionId}" serverurl="${sf.serverurl}" maxPoll="${sf.maxPoll}" retrieveTarget="retrieveUnpackaged" packageNames="mypackagename"/>
</target>

...and to deploy...

<target name="deployCode">
  <sf:deploy username="${sf.username}" password="${sf.password}" sessionId="${sf.sessionId}" serverurl="${sf.serverurl}" maxPoll="${sf.maxPoll}" deployRoot="retrieveUnpackaged" rollbackOnError="true" testLevel="NoTestRun" singlePackage="true">
  </sf:deploy>
</target>