PR is not measured by back links alone as everyone here has pointed out. Silveraden has posted a good resource to get quality backlinks. I'll try them out myself.

try to get a website with baclink from pr4, pr5, pr6

There is no such forumla to tell u howmany backlinks are need to get a PR X, it is all about the quality.

I don't think there is such forumla that tell u how many backlinks equal a PRX.

The point if to build high quality backlink from related niche!

It depends on the quality, relevance and PR of the sites you are getting links from. Actually saying, nobody know Google's PR algorithm so continue link building untill you achieve your desired PR.

Research the market, industry, competitors, etc and find high PR, relevant links that provide value to potential customers.

There is no formula but look into the number of outgoing links on the page and if they are 'do follow' links.

1 PR 6 related link can be worth more than 1000 PR1 unrelated links

The quality, the relevancy are how google juge your site, so I think as long as u can guarantee these, then the more the better!

I have a follow on question - can you expand on exactly what inner links and inner pages are? Is this the same thing as deep linking when you are linking to "sub pages" and "sub-sub pages"?

For making it PR4 or 5 you may need 3k to 4k backlinks but it also depends on the sites names and keywords.

hey, you should exchange links with high pr webiste, then your pr will higher than before