I have a site that uses pMachine for blogging, vBulletin for forums, and Indexu for a directory. Isee that plugins are available for all of these -- does that mean that I could install aMember and each plugin and I will have a single membership system across the entire site: one registration and one login page?
Yes, if user registers in aMember, he will be registered in all your integrated scripts. And, if user logs-in using aMember login page, he becomes logged-in in all these scripts. Unfortunately, NOT VICE-VERSA.