All of our diving is at the oil rigs and mostly spearfishing.  Charters are
nearly non-existent.  You could try http://www.rodnreel.com/xtreme/
Boats leave at dawn and return at dark; long boat rides to good water.  No gear
rental.

You have all of Lake Pontchatrain to dive in... Max depth of perhaps 12 ft,
visibility measured in feet on a good day, inches on a bad day... There's
also the Mississippi River to dive in... Max depth probably around 70 ft if
you are in the middle of the channel (try not to pay any attention to the
screws of the large cargo ships passing overhead that have been known to get
a little extra traction in the shifting sands of the river... Visibility
measured in inches on a good day, fractional inches on average days, and
millimeters on a bad day... It's a pretty long drive to get out to the Gulf
of Mexico and you have to get away from the muck that the Mississippi River
dumps into the Gulf before you will get any good diving... Probably around
30 miles offshore will allow you to get to blue water... There's plenty of
oil rigs off the coast, so there's good diving if you are within the legs of
the rigs, otherwise, you have basically a mud bottom...

Or you could drive over to the Florida panhandle for some cave diving...
It's not that bad of a drive in that you don't even have to leave that early
in the morning to get there in time to do some early afternoon diving and
then drive back to New Orleans that night... From New Orleans to Vortex
Springs (located near Ponce de Leon, FL) is around 280 miles -- about a 4 to
4.5 hr drive... Water temperature is around 70-72F year-round...

If you are going to have a car, you can get a lot cheaper hotel rates by
staying a little further out from the CBD (Central Business District)...
Where is the conference located?  If it's not at your hotel, you might find
parking an interesting experience around the CBD and the French Quarter...
The signs saying where and when you can park can be rather confusing to the
newcomer... A hotel not in the CBD might go for $40 per night, especially if
you are going to be renting it for an entire week... New Orleans is not that
large, so even at the very outskirts of the metroplex to the west (Kenner),
it's not a bad commute into the CBD (30-60 minutes depending upon how many
wrecks are on I-10)...

There's some local shops around here, so I suspect that you could rent
whatever gear you might need... If you go to Vortex Springs, you can rent
everything that you might need over there from what I understand... I own my
own gear, so I'm not positive on this, although they do seem to have a
rather complete dive shop over there... Vortex Springs does have a nice
campground and you might want to consider checking out of your hotel after
the conference and either camping there or staying at some local hotel...
Hotels are plentiful enough that you don't need reservations, just make the
dive and wing it on determining where to stay afterwards... Personally, I
would suggest checking out of your hotel on the morning of the last day of
the conference, driving over to Florida that night, finding a hotel
somewhere around there, and then spending the next 3 days diving around
there... If you are wanting to dive in the Gulf, Destin, FL is probably the
closest place to New Orleans that has pretty good water... Although I've
never dove from there, I believe that I've heard it mentioned by some of the
Florida natives here on rec.scuba...

SouthWest Airlines... 100-200 round trip to Fort Lauderdale or West Palm
from NOLA ... real diving, rental gear and LOTS of charters.   I lived
in NOLA for four years, I got my OW there and besides the trips to
Biloxi and Pensacola (bad vis and shallow dives) there wasn't much there.