I've got a DSC-P100 that I'm very happy with. Pics here: http://www.fauncefamily.net/album
I'd skip the DSC-P93, it's going to have lag and other "last generation" issues. The DSC-P93 is actually several generations behind (P93-> P10 -> P100/120/150 (same cameras at 5/6/7 MP) -> P200)
I'm planning on getting a P150 for my wife as it uses the same housing as the P100 and she's getting tired of the lag and response time on her P10. I'd get a P200, but there isn't a housing and according to Sony support desk, there isn't one on the horizon either unless the successor to the P200 uses the same body -- like the W series, the housing with introduced with the W7 and worked with the W5 and W1 since they use the same body.
Inon also has a kit to allow their strobes and external lenses to work with the MPK-PHB housing that the P100/120/150 use so you have an easy "growth" path with that system.
A 256MB Pro card holds just over 100 pics (I usually get about 110-115 before filling the card). I've played with the video part, but haven't really used it, so I don't have a clue how much video a 256MB card would hold.
As someone else stated the battery in the P100 holds a charge pretty well. I typically fill the 256MB card on two dives and the battery is still going strong, even with forcing the internal flash on every shot. I've got 2 batteries and an external charger, so I swap batteries when I empty memory stick.