I'll keep this one nice and short - and hopefully save a couple of people participating in a bit of self inflicted baldness! Installing the TinyMCE module (a nice WYSIWYG editor) in Drupal 5 should be a breeze.
You then enable the module as you would any other.
You now need to ensure you have at least 1 role created - AND ensure that the admin user is a member of this role (if you intend for them to use the tinymce editor).
You will then need to goto admin/settings/tinymce and create a "new profile", ensuring that you enable the profile for your new role. Also make sure you have at least 1 of the buttons ticked to show.
Now for the fun bit. If you are logged in as user 1 (the admin user) - you need to make sure that you explicitly put yourself into the new role you have created. This caught me out, as I am so used to the admin user having all permissions!
And thats it, you should be good to go ...