McFeasty:opensource Stig$ ~/apache-maven-2.0.9/bin/mvn archetype:generate -DarchetypeGroupId=org.grails -DarchetypeArtifactId=grails-maven-archetype -DarchetypeVersion=1.0-SNAPSHOT -DarchetypeRepository=http://snapshots.repository.codehaus.org -DgroupId=example -DartifactId=my-app
[INFO] Scanning for projects...
[INFO] Searching repository for plugin with prefix: 'archetype'.
[INFO] ------------------------------------------------------------------------
[INFO] Building Maven Default Project
[INFO]    task-segment: [archetype:generate] (aggregator-style)
[INFO] ------------------------------------------------------------------------
[INFO] Preparing archetype:generate
[INFO] No goals needed for project - skipping
[INFO] Setting property: classpath.resource.loader.class => 'org.codehaus.plexus.velocity.ContextClassLoaderResourceLoader'.
[INFO] Setting property: velocimacro.messages.on => 'false'.
[INFO] Setting property: resource.loader => 'classpath'.
[INFO] Setting property: resource.manager.logwhenfound => 'false'.
[INFO] [archetype:generate]
[INFO] Archetype defined by properties
org.apache.maven.archetype.downloader.DownloadNotFoundException: Requested download does not exist.
        at org.apache.maven.archetype.downloader.DefaultDownloader.download(DefaultDownloader.java:62)
        at org.apache.maven.archetype.common.DefaultArchetypeArtifactManager.exists(DefaultArchetypeArtifactManager.java:310)
        at org.apache.maven.archetype.ui.DefaultArchetypeGenerationConfigurator.configureArchetype(DefaultArchetypeGenerationConfigurator.java:103)
        at org.apache.maven.archetype.mojos.CreateProjectFromArchetypeMojo.execute(CreateProjectFromArchetypeMojo.java:168)
        at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:451)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:558)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeStandaloneGoal(DefaultLifecycleExecutor.java:512)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:482)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:330)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:227)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:142)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:336)
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:129)
        at org.apache.maven.cli.MavenCli.main(MavenCli.java:287)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:585)
        at org.codehaus.classworlds.Launcher.launchEnhanced(Launcher.java:315)
        at org.codehaus.classworlds.Launcher.launch(Launcher.java:255)
        at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:430)
        at org.codehaus.classworlds.Launcher.main(Launcher.java:375)
Caused by: org.apache.maven.artifact.resolver.ArtifactNotFoundException: Unable to download the artifact from any repository

Try downloading the file manually from the project website.

Then, install it using the command: 
    mvn install:install-file -DgroupId=org.grails -DartifactId=grails-maven-archetype -Dversion=1.0-SNAPSHOT -Dpackaging=jar -Dfile=/path/to/file

Alternatively, if you host your own repository you can deploy the file there: 
    mvn deploy:deploy-file -DgroupId=org.grails -DartifactId=grails-maven-archetype -Dversion=1.0-SNAPSHOT -Dpackaging=jar -Dfile=/path/to/file -Durl=[url] -DrepositoryId=[id]


  org.grails:grails-maven-archetype:jar:1.0-SNAPSHOT


        at org.apache.maven.artifact.resolver.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:212)
        at org.apache.maven.artifact.resolver.DefaultArtifactResolver.resolveAlways(DefaultArtifactResolver.java:80)
        at org.apache.maven.archetype.downloader.DefaultDownloader.download(DefaultDownloader.java:54)
        ... 21 more
Caused by: org.apache.maven.wagon.ResourceDoesNotExistException: Unable to download the artifact from any repository
        at org.apache.maven.artifact.manager.DefaultWagonManager.getArtifact(DefaultWagonManager.java:331)
        at org.apache.maven.artifact.resolver.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:200)
        ... 23 more
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] The desired archetype does not exist (org.grails:grails-maven-archetype:1.0-SNAPSHOT)

[INFO] ------------------------------------------------------------------------
[INFO] For more information, run Maven with the -e switch
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3 seconds
[INFO] Finished at: Thu Nov 13 07:39:26 CET 2008
[INFO] Final Memory: 8M/508M
[INFO] ------------------------------------------------------------------------