When installing into Helios you will get the following error:
Missing requirement: Maven Integration for Eclipse (Editors) 0.12.1.20110112-1712 (org.maven.ide.eclipse.editor 0.12.1.20110112-1712) requires 'bundle org.eclipse.zest.core 0.0.0' but it could not be found
You have to install the editor from here first;
The part which isn't on the internet:
Pick the latest release and install ONLY the complete SDK. The rest of the modules you don't need. I hate Maven because it downloads so many files into both eclipse and my repository, I can't keep track of what is where. At some point I need to dig into it but that is time I'd rather use somewhere else.
Then you can go back and install Maven.