I’ve experienced an issue with NextGen Gallery v1.7.2 and Word Press v3.0.4. Editors were able to create galleries, but when trying to include a gallery to a post, the selection process wasn’t working.
Seeing the trouble I’ve tried to downgrade to v1.7.1, then to v1.7.0 and only when I came back to v1.6.2. the bug disappeared.
I would recommend you to use v1.6.2 for now ??