I guess perhaps we're not on the same page here. I made an assumption and it appears to have been the wrong one.
When a user registers they are not fully registered until they are validated (meaning they have no real group until their account is validated) and they are put into the default members group (which I thought starting this, was your validation group like they join the site and you make sure their posts are okay or whatever). Promotion rules are intended to move groups or add/remove secondary groups based on the criteria.
If you need a group between Validating and full member you need your default members group to be that group and promote them out of that group into another group.
So first off, by default once the person is validated (depending on your validation method) they are automatically placed into a standard "Members" group. Before they are validated they are queued to either be approved or deleted depending on validation settings.
If you want to move them to a new group immediately after they are validated you just need to add a group promotion rule that you leave everything default except the "move group" setting which you choose what group you want them to get.
