I had a similar situation and I managed to pull it w/o creating new project.
Modified the .classpath to include this
<classpathentry exported=”true” kind=”con” path=”org.maven.ide.eclipse.MAVEN2_CLASSPATH_CONTAINER”/>
Modified the .project to include this
<nature>com.genuitec.eclipse.maven.maven2Nature</nature>
Voila~ now I enabled my existing project w/ Maven!