Ah, good old relative and absolute size.
Anything labelled with dpi, lpi or ppi is relative size, which only bears if you have to stretch or compact the pixels in your image to a pre-defined standard. The number of pixels in your image is absolute - there's no more, no less.
Despite us buying monitors based upon their physical dimensions - 17", 20" asf - they are really absolute, that is like your image they have a specific number of pixels, no more, no less. Hence your image is shown pixel by pixel, not in relation to inches.
Thus, relative size comes into play when printing, since paper does not consist of discrete pixels but is an analogue medium defined by its physical dimensions.
Let's not dwell too long on the differences between dots, pixels and lines, just say the first two are 1:1 equivalent, the latter stands in a 1:2 relation and is only necessary to know for professional printing houses. Your printer translates the pixels of your image into [many-layered] dots.
Every inkjet printer has a physical limitation - the number of tiny holes through which the ink is pressed. This is its native resolution, depending on maker this goes from 240 to 360, with some higher end Epsons having 720, Canons and Hewlett-Packards can go up to 600. That's all dpi.
The higher numbers touted for printer res, i.e. 1440 and 2880 for Epson, are shorthand for the multi-layering resulting in smooth gradations.
While image files usually contain a relative resolution number, from 72 to 300, this has no meaning. AFAIR, only Photoshop might use it as the default when you print but forget to set the relres.
For your photography that means: don't fret over relative resolution. It has no bearing on taking the picture. What you should fret over is your technique. Use a solid tripod with an even solider [sorry] head, stop down your lens two or three stops but not more unless absolutely necessary [same holds in the opposite direction], use a remote release, etc.
PS: If you are interested to learn more about printing with SOHO devices, you might want to have a look at Mike Chaney's column over at
Steve's Digicams under Tech Corner.