Here's a page describing Georgia Tech's entrant to the Eighth Annual AUVSI and ONR Autonomous Underwater Vehicle Competition,   This model actually took 12th place in the competition, which ran Aug. 3-7, 2005, with the University of Florida's Subjugator taking first place.

The Georgia Tech students describe the design and construction of their pretty functional-looking AUV.  There are photos and schematics and in the end you actually get to see the craft in the water.

  http://www.linuxdevices.com/articles/AT7101484471.html

You can build a glider that works underwater, much like a sailplane works in the air.  Really.  It'll fly like a glider too, with gravity pulling it along as it descends.  Sure there are differences between an air and a water glider.  The underwater version will have smaller wings than you might expect because of how dense water is compared to air.  And it's probably not going to move that fast...

In terms of suitability for a people-carrying, homebuilt type project, well I don't know.  One apparently very successful example is Karl Stanley's CBUG which he's used for years as a tourist sub.  See the link below and check out Mr. Stanley's photos and track record as a tourist sub builder and operator...

As the title says, the 8th International Autonomous Underwater Vehicle Competition has wrapped up in San Diego, California.  First place was taken by the University of Florida, second by Ecole de Technologie Superieure of Montreal, and Massachusetts Institute of Technology in third place.

The AUVs, or their teams, were given a set of missions to complete:

• Rendezvous with a 'docking station'
• Find and mark a break in an underwater pipeline
• Home in on an acoustic beacon and surface within a marked zone

AUVSI website...

Florida Subjugator website...