I have the exact same issue. The doc doesn't say the reporting against baseline feature isn't available in Enterprise edition but I sure don't see it. Sold my boss on implementing baselines based on, amongs some other capabilities gained by implementing baselines, the ability to report against baselined entities. ALM has made a liar out of me. Wassup with that?
I'm thinking it must be a Premier / ALM Edition only feature rather than Quality Center Edition and the doc left that important piece of info out.
Anyone out there with Premier / ALM Edition that can confirm / deny the Select a Baseline option is there in Project Reports?