Nikon D3100 Questions

I think Bryster covered the first half, I'll take 4 &5:

4) Turn off VR when you're on a tripod, it'll actually make your shots blurrier.
5) I don't know how this works on the D3100, but on my D7000 if you turn the dial you can bias P towards aperture or shutter speed. Try messing around with that (you should be able to get to P*)

I use Lightroom for photo management. It's much cheaper than buying CS5, and it can convert your RAW files into Adobe's RAW format. It's slightly smaller, with 0 loss in data. Also, it can be imported into my version of Photoshop (CS4) with no problem.

Personally, if you've got Photoshop, I wouldn't recommend buying another photo editing program. Lightroom is quite expensive, but it's worth every penny.

In order to understand the difference, and why to use DNG, it's important to know some stuff about the RAW formats that DSLRs shoot in.

.NEF is Nikon's proprietary closed-source RAW format. In order for an application to read it, the application's maker is required to pay money to Nikon so they can licence it for use in the program. Different cameras also use slightly different RAW formats, so if a newer Nikon camera comes out, it may still use .NEF, but a program may be able to read your camera's RAWs but not the newer ones. It's the same with all DSLRs when shooting in RAW. Compatibility cannot always be guaranteed when using manufacturer specific RAW files.

Then there's DNG. It's Adobe's Digital Negative format. Open-source so anyone can use it in their programs. There's no licence fee or anything to include it in a program, so there's plenty of incentive for people to include DNG compatibility. Not only that, but it standardises all RAW formats into one. If you get a new DSLR, you won't be faffing with slightly different RAW formats over multiple cameras, but instead they'd all be in just one.

The final reason is for archiving. In 20 years, it's highly unlikely that the photo editing software will have compatibility for our cameras. If you ever wanted to look at your photos, you'd need to find some kind of conversion software, because our cameras would be too old for software makers to consider it worth licensing the plugins for our specific model. DNG is designed to always be readable and is meant to be future proof. Since it's made by Adobe, and they're the makers of the most popular photo editing software available, it's a slim to none chance that they'll ever stop support for their DNG format.

Also, for my RAWs it shaves a few megabytes off. Always worth it when you've got 7000 photos sitting on your hard-drive

EDIT: and yes, it is completely worth it. I think there's a free trial available? Not sure though, my be confusing it with some other software. Once you get used to it, you can do most of the stuff you'd expect to be able to do in photoshop, but easier and across multiple photos. It can also correct lens distortion automatically, which is nice.

No idea, I'm afraid. When I import my photos via Lightroom, it automatically converts to DNG and sorts it into folders for me so I don't have to worry about it.

Adobe usually provide one though, have you tried http://www.adobe.com/support/downloads/detail.jsp?ftpID=4576 this? It specifically states it supports the D3100.