An internal link is an in-coming link from within your own site and although it does not have as much weight as an external in-coming link, it still can help.
The Google PR of your internal pages help with internal linking and, therefore, the way you pass and distribute Google PR throughout your site via absolute vs. relative URLs does have a small influence on ranking.
It is always still important to link within your own site in a way that makes sense to your visitors and not just with search engines in mind only.