Hi,
In WSS 3.0 , you can add web part without having to create *.webpart or *.dwp first. WSS 3.0 will do it for you on the fly. I saw some missing action from your steps,
1. Deploy *.dll to bin of web directory (done)
2. Add SafeControl to web.config of the web (done)
3. Add web part to web part collection <=== (not done)
4. Try to add web part to page <== error
To add web part to web part collection you need go to "Site Action" | "All Site Settings". Then go to web part collection gallery. Or "**_catalogs/wp/Forms/AllItems.aspx" for your short cut. (replace ** with url of SharePoint site).
Regards,
Riwut Libinuko
-htto://www.plasmedia.com-
*please rate me, if this post is helpful
Best Regards,
-Riwut Libinuko-
SharePoint Architect, Singapore
cakriwut@gmail.com