Well... I've been working on posts and have noticed that the whole Drupal database has changed form as I've added content types. Here's what the node tables look like now:
So what's happening? Node data always gets entered into node and node_revisions, as before. But for content types, one of two things happens.
If a content field, such as 'description', is used in two or more content types, then a special data table, node_data_field_description, is created for that field, and the data stored there.
Otherwise, the data is stored in a field reserved for the data type itself, such as node_content_post.
No great disaster, I'm just glad I found this out now. It means some changes to the script, nothing major.
I also discovered that my post database is 17 megabytes large. To load it, I saved it as an SQL file, uploaded by FTP, then ran the command:
mysql -u username -p databasename < post.sql
Worked like a charm.