The "Vault Radio" already plays them, but you need a DSL connection to listen, because they stream at 128 kbps MP3, otherwise you don't hear anything (like me) or only stuttering:
http://www.wolfgangsvault.com/Static.aspx?Type=Audio/Radio.htm&CategoryID=RA&LeftNav=Audio/RadioNav.htm&nhbx=1
From there you can also leave and/or read some great feedback of people who have been there:
http://www.wolfgangsvault.com/VRFeedback.aspx?LeftNav=Audio/RadioNav.htm
Also in the weblog of the site owner:
http://www1.wolfgangsvault.com/blog/CommentView.aspx?guid=__
The story of Bill Graham and his estate is also published on their site in five parts:
http://www.wolfgangsvault.com/About.aspx
http://www.wolfgangsvault.com/About.aspx?Type=lastdance.htm
http://www.wolfgangsvault.com/About.aspx?Type=BillGraham.htm
http://www.wolfgangsvault.com/About.aspx?Type=PosterArt.htm
http://www.wolfgangsvault.com/About.aspx?Type=Performer.htm
I also hope that those live recordings from the Fillmore will be available on CD or DVD soon, e.g. Cream, Led Zeppelin, Allman Brothers, B.B. King... Interesting detail is that Jimmy Page is keen to dive into this archive since he compiled the Led Zeppelin history on DVD, and that the estate owner Bill Sagan was in London recently talking to some lawyers already.
Just found a passage on a ZZ Top related site which could be very interesting if Bill Graham has taped that well-known show, too:
http://www.famoustexans.com/zztop.htm
In an event that tried to be a rock-style Willie Nelson Picnic, the group was the featured headliner in the "Rompin' and Stompin' Barndance and Barbecue," held in Austin on Labor Day, September 1, 1974. Appearing with them before a crowd of 80,000 was San Francisco legend Bill Graham, Santana, Joe Cocker and Bad Company making its U.S. debut. This was ZZ Top's first concert in which they were seen as more than just a Texas act. It was the biggest concert in Austin's history, and the last to be held in Memorial Stadium on the University of Texas Campus for another twenty years. The stadium had been trashed by concert-goers, who had suffered from the heat and lack of food, water and toilets.