Internal site links will have some effect, but it's more a part of your onsite seo the same as using tags correctly, having good content, etc. It's known as PR sculpting and should be considered as part of your overall site design. It isn't as big a deal as it once was but it's still a good idea to set it up correctly for your onsite seo . Basically you want to make sure you have links pointing to your main page from all you subpages. That's kind of a no brainer that everyone does. It can also be a good idea to have a few links from some articles on your subpages to other articles on the site that you want to be seen as more prominant. You also want to set up your links to pages like disclaimers, about me, and other similar content as no follow. If you do that then whatever link juice is flowing internally through your site won't be wasted on pages like 'about me' and can be concentrated on your actual content pages.
Doing all that will only have much effect though if your deeplinking in your backlinking campaigns.
If you do a google search for PR sculpting you can learn a little more about what the best practices are.
