OpenACS 4.5 will be released very shortly. I've tested the final tarball and will be ready to announce availability after checkoff by e-mail with a couple of folks.
dotLRN requires the development head of OpenACS 4, and will not work with the OpenACS 4.5 release. We plan to push for a stable 4.6 soon after dotLRN itself becomes stable under Oracle and PG.