Saz
dpi (or ppi) doesn't matter for web work. Just the overall pixel width & height.
Where it does matter is at the time of export. If your using a program who's basic resolution is 96 dpi, and you've adjusted your image to the size you want it when viewing at 100%, then exporting it at 96 dpi will export it at the exact same dimensions as seen on your screen.

If you export it at 72 dpi, the image will be smaller than the original. (So of course the file size will be smaller also!)

However if your using a Mac ported program on a PC then this might use 72dpi as it's native resolution, then you may need to export at 72 dpi to maintain the same size as this program.

Other than the above, dpi means nothing for web production.

See this

Egg