How to configure "tomcat7-maven-plugin" in pom.xml?

The Tomcat7-maven-plugin should be declared as a plugin, it is not a dependency. You can't add a configuration tag to a dependency as indicated by the error.

Thus something like the following should work :

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.tastyminerals.poems</groupId>
<artifactId>poemcollection</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>war</packaging>
<build>
    <plugins>
        <plugin>
            <artifactId>maven-war-plugin</artifactId>
            <version>2.3</version>
        </plugin>
        <plugin>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.1</version>
            <configuration>
                <source>1.7</source>
                <target>1.7</target>
            </configuration>
        </plugin>
        <plugin>
        <groupId>org.apache.tomcat.maven</groupId>
        <artifactId>tomcat7-maven-plugin</artifactId>
        <version>2.2</version>
        <configuration>
            <url>http://localhost:8080/manager</url>
            <server>localhost</server>
            <path>/${project.build.finalName}</path>
        </configuration>
        </plugin>
    </plugins>
</build>
<...>
   </project>