I have a pretty old DotNetNuke installation which is broken (in more than one way) and won't let me upgrade. I've set up a new installation and want to move the content. The old portal has a massive amount of data, so moving it manually will take very long.
Is there any way of migrating between portals without manually copying?
I know tools exist to do this between SharePoint portals.
I'm capable of doing SQL and even writing a few lines of code if required.
It depends on where your data is stored. Some modules will implement the "Portable" feature, which means that you can export them with content. However, there's not even a great way to export all of your content at once. You can export a portal template (from Host -> Portals), but if you're upgrading a lot of versions, the new version won't be able to handle the old version.
If your information is in a lot of different modules that don't support the "Portable" feature, you'll need to consider each of those modules separately (probably doing some sort of SQL export specific to each module).