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Within a closed system (such as a site with no inbound links), various linking stuctures can be used to manipulate PR and provide a boost to certain pages. Sites with many pages are better positioned to take advantage of this phenomenon than are small sites, because they have a bigger pool of PR to throw around.
Internal linking structure is important. I have a PR6 page and I made some "smart" changes and removed many links that pointed internally to different sections and pages of my site.
Result: Three months later, I lost between 10 and 30 positions in most keywords.
So, take advantage of your most important page and use it to link internally. It is not a matter of how much page rank you will be passing to internal pages. It is a matter that you are linking them from an important page that has the same theme. Perhaps it is the same as passing page rank, but I like to think of it in terms of logical organization of links and topics.
Another thing. Keep those links for a long long time. Don't remove them.
When my page rank was raised from 5 to 6, my homepage didn't get more traffic, but in general my whole site started to receive more traffic due to links pointing from my homepage. Now I removed them and I still have PR6 but 40% less traffic!
Hope this helps.