Actually, you don't need the old database at all. This is how I did it..
Export your data out as an XML file (use the "all" authors setting if there's more than one)
Delete (or move to another directory) the version 2.5 files
Create a new database
Upload the version 2.3.3 files, and install as "new"
Log in and delete the placeholder post ("hello world"). Also make sure that you re-create all the author names, if there is more than one.
Import in the XML file. (NOTE: If you have a lot of data, you may need to adjust the "upload_max_filesize" setting in php.ini..if you don't have access to this file, contact your host..my host was very cooperative)
That should do it. In my case, my theme was slightly out of whack, but nothing big.
Good luck, and long live 2.3.3!