As many posts here state, DPI is largely meaningless UNLESS you are using something like photoshop. In that case, if you tell Photoshop to show you the 'print size' of a picture tagged 300dpi, it SHOULD display the picture on your screen at the same size it will be printed if your settings to print are similar. So, if your 300dpi image on screen is four inches by five inches your 300 dpi printout is a 4x5 too. That's pretty much all DPI is good for with regards to normal non-pro consumers.
That only worked while all monitors had 72 PPI, nowadays with PPIs varying a lot between different monitors that function is of little use in my opinion.
In general, DPI is an indirect way to tell the printer how large an image should be printed. Instead of saying print this image 6 x 6", you tell the printer to take a 600 x 600 pixel image and print it at 100 DPI.