Hey Steve
I think your best bet is to get a camera that writes to tape as opposed to an HDD if you want to keep a lot of your footage. Trying to back everything up on HDD gets to be a pain down the road if you ask me (my opinion only...) as HDDs are a lot more expensive than tapes...
With tapes you simply use a firewire connection out of the camera and into the PC.
As you are probably aware there are two popular formats these days. HDV and DV, HDV has great benefits of resolution and quality but lacks popular end support such as the fact HD DVD players are only now coming out so it is difficult to share the actual quality of your HDV stuff with others. There are ways around this but if you typically send DVDs etc to friends/family you will end up downgrading your HD stuff to standard DV but this will probably be of higher quality as well.
I will give a Sony bias here as i am not familiar with the Canon line up that Drew knows well so he can wade in with info on those later.
So, depending on your budget and needs you can probably find some really good deals on used mid range DV packages of camera and housings around. Popular ones to look for would be the Sony VX2000 or VX2100, Sony PD150 or PD170 and the Sony TRV950 and PDX10. Popular housings for these cameras include Amphibico, Gates, Light and Motion, and Sea and Sea among others.
I think any of those camera/housing combos would be a great deal for you.
IF you want to go with HDV then you have a few options in ither entry level or top level but not a lot in mid range at the moment. The first mid range product is now out, the Sony FX7 but housings are not available as of yet. There is a great thread about this camera here: http://wetpixel.com/forums/index.php?showtopic=15081
This may end up being the camera that fits your needs, but you will have a few months to wait for the housings to become available and get some useful feedback on them.
As for software, some to think of are Sony Vegas, Pinnacle Studio, Premiere Elements, and Canopus Edius. I believe all are available as a 30 day trial so you might want to use a few trials to see which interface you like the best and is most intuitive to your style.
A website that give reviews on cameras is:
www.camcorderinfo.com