If your Movable Type installation uses extra fields and you want to use MT4, then at this point, you really only have one option – Custom Fields. The plugin, currently in something of a perpetual beta because Arvind is in the US for school, allows you to easily add fields to just about any object in the system. It’s actually quite nice.
But if you have already been using Custom Fields, you might find yourself in a bit of a pickle when it comes to upgrading your data and you’ve found that the data you have been trying to keep from losing is suddenly no longer there. Luckily, the upgrade path isn’t a bad one, nor is it particularly painful. You just have to be very careful when you decide to upgrade your installation.
First, upgrade Movable Type. You won’t be able to use Custom Fields, because the plugin hooks are different, but it will mean that you don’t have to worry about any standard upgrade problems getting in your way.
Next, upload the files from the beta to your server. Also, make sure that you have the CustomField.pm file. You can find this in the lib/CustomField folder of your original plugin directory, and you’ll want to make sure it’s in the same location. If you don’t have it there (for instance, if you delete the old directory and upload the new directory), then the plugin will install, but the upgrade won’t happen!
If this is the case, then it’s a real bear to get your data back, because the plugin version is upgraded, and even if you put the file there, it won’t realize that it needs to upgrade the data. So make sure you get the file and put it in the right location before you run the upgrade.
Once you have the file in place, log into Movable Type. You’ll be prompted to login, at which point your data will be upgraded. Make sure you take a look at the custom fields that you have configured, because some of them will not transfer over. For instance, the file upload type that was previously used doesn’t work, so you’ll need to go into that field and change it to a new type. After you have verified your fields, you’re all set!