I want to move some articles from an existing J! 2.5.x installation to another J! 2.5.x installation. I have had a look in the extensions but there is not a non commercial component that does this.
Can anyone provide any suggestions?
If you're talking about a one-off migration of articles there are a few options available. We use a variety of extensions depending on the job requirements, they are all listed in the Joomla! Extension Directory's section for Migration.
Lately we've been using the SP extensions more as we've had good experiences with their tool for migrating clients sites from Joomla! 1.5 to 2.5.
We used their SP Transfer twice to migrate groups of articles where a client had decided to break their website up into several smaller sites.
We've also used CSVI but that required a bit more manual work with respect to linked images and files.
Why don't you duplicate entire DB and remove articles you don't need? In case if another installation is fresh install.
From command line you can export and import DB: