Hey Monkey_Knife_Fight! 

Welcome to the briney.
My feeling is that you would be better served in the longer term by housing an S60.
Both the A95 and S60 are very similarly spec'd and priced, but there is one key difference - S60 does RAW. Now, topside, this is relatively less of an issue, but UW it can be a bit of a problem.
Primarily, the difficulty lies in the handling of white-balance (WB). Topside, you can easily measure WB and then set the camera appropriately. UW, you want to maximise the time you have down there actually shooting and therefore it is extremely handy to be able to set the WB after the dive. There are of course a number of other significant benefits to shooting RAW in terms of post-shot handling of sharpening/tone/curves etc., which can also add to the overall image quality of a shot. Now, that's not to say it's all good...
Shooting RAW means big files and therefore longer write times and also more processing time once you get out of the water. Guess it really depends on what your expectations are and how picky you are with image quality.
Both the A95 and S60 will accept external UW lenses and strobes from INON which makes them appear quite similar. However, currently only the A95 can accept a wide-angle (WA) lens. INON have developed an UWL100 28AD specifically designed for cameras like the S60 that have a 28 mm native lens. But this lens is not scheduled for release until May 2005. In the mean time you will need to do macro or (not very) wide angle
Most people reckon that it's good to start off doing macro anyway (easier to get good results quickly) and then move to WA once you get more confident/skilled.
So in summary...both these cameras are a good choice for UW, but the S60 is better in a number of areas and will probably serve you better in the longer term if you get into UW photography.
FWIW you might also consider the Fujifilm F810 which is slightly less expensive and is a popular camera to house. Advantages of the F810 over the Canon are (slightly higher) resolution, RAW file handling, low light AF, ability to attach wide lens available now (INON 105AD). Advantages of the S60 over the F810 are battery life, cheaper/larger storage media available and ability to use S-TTL (fully auto) with INON D2000 strobe. The F810 can only do "external auto flash" where the strobe is working independently of the camera (may not be as accurate under some circumstances).
HTH