Single Sign on Solutions on the (Very) Cheap?

ATMosby asks: "I was asked today to look into how a single sign on can be implemented. Now part of the constraint is that is must be very cheap (and by that the powers that be really mean free!) Of course there are all sorts of legacy applications that are 'required' to work with this, ranging from java applications to ancient pc programs. I've poked around a bit and found some pointers to commercial software that seems to be able to due bits and pieces of the job, but nothing that will do everything and anything that might be thrown at it. Before I just go and tell folks "No bloody way!" does anyone have words of advice to offer on the topic? Stories of successful or wildly unsuccessful attempts? Commercial or otherwise?"