Normally for print you would use the 300 dpi version as a tiff (a 300 dpi jpg is fine in most cases as well). The jpg file format just has less color info.
Normally you will find jpg images on the web. 96 or 72 dpi.
Yes, or 72 is very common also.
That is correct. The only case were you will obtain 300 dpi quality is to maintain file size. In other words if you took a very large 96 dpi pic and converted it to a very small size dimensionally at 300 dpi it would look decent. It is all about color information in the original file. You cannot take an 8" wide 96 dpi picture and convert it to and 8" wide 300 dpi picture for printing. Simply doesn't have enough color information in the file to do this successfully. It will come out very blurry or grainy. You can downsize but not upsize (much).
The large pics you linked to would be great for print. They look great online too but file size is huge for the internet at well over a meg. If you view a 96 dpi version on screen you probably will see little if any quality difference. The large file size makes for very slow loading of anyone viewing the pic. If they were embedded in the forum page with bb code the entire page would load slowly even on dsl. For anyone with dial up, fogettabouit.
The dpi or dots per inch does not determine width. It only determines the dots per inch or the color information contained in one inch. In printing everything is dots of ink per inch. If you look through a loop or magnifying glass at print work you will see the little dots. This is what dpi is. At less dpi the image gets grainer to the eye. The human eye cannot see 300 dpi as dots on paper. But as it becomes less dpi you can so in turn the picture looks grainy. At 72 dpi (printed) you can see the actual dots because they are far apart.
On a computer screen it's different. Everything is pixels. There are screen pixels and image pixels (dpi). The human eye can't differentiate anything much greater that 96 on screen as that is the screen pixels. Anything greater dpi and you can't tell much if any difference. Try saving a picture at 30 dpi and view it on screen and you will get the effect. It will be very grainy. View the same pic at 300 dpi on screen and you'll have trouble telling it from the 96 image in most cases. Screens vary.
Hope that explains more than confuses. :huh: