Since I just spent a good chunk of time looking for this info I figured I would post it, since I can't find it anywhere.

the table sequences houses code based auto increment values for the various nodes or counters. For example it makes sure node 114 follows node 113. entries are made the FIRST time a node is created, they are not created with the database install.

the table node could be considered the administrative location of node information. It has things like "is this node sticky" and who created it, and so on.

The table node_revisions contains the actual content, managed by all these other tables. this is where your entries are stored by drupal when you make content.

This is quick, and related to conversion scripting from phpnuke to drupal. sorry it isn't more complete, but if we all build on this info we can have a working table description eventually.

This is REALLY IMPORTANT if you are doing something stupid like trying to host 10 sites in one database and converting some from phpnuke to our friendly drupal