I had problem adding a webpart to the webpart gallery too.
I have to reboot the machine to add a webpart in the "add new webpart to a gallery" list.
I can't get a refresh if I change the webpart in VS2K5 (and re-generate it).
I don't have a intpub/wwwroot/web.config, so I modified the web.config or every virtualdirectory.
I use MOSS2007beta2 (without tech refresh) and WSS3. French version upgraded form Sharepoitn server 2k3.