Page Rank IS a measure of the number and strength of your backlinks. But simply having backlinks and/or page rank is NOT going to make you rank.
The key to ranking in the SERPs is having backlinks (regardless of the PR of pages linking to you) that use the keyword phrases you want to rank for (or slight variations) as the anchor text or link text in the hyperlink. Having such links is probably the MOST important ranking factor looked at by Google.
I can make a page about turtles rank for “elephants” if I get enough backlinks from relevant sites with “elephants”, “elephant”, “elephant trunk”, “elephant sounds”, elephant dung”, etc. in the link text even without the word elephant every appearing on the turtles page. If those backlinks are from high PR relevant sites w/ “elephants”, “elephant”, “elephant trunk”, “elephant sounds”, elephant dung”, etc. in the link text, then that’s even better.
I prefer links from relevant pages w/ relevant link text over links from irrelevant high PR pages w/ crappy link text any. I would take 1 PRO link from a site about my topic w/ the keyword phrase I want to rank for as the link text over 10 links from PR5 pages that are not about my topic w/ “click here” as the link text. Those PR5 links w/ link text of “click here” are only going to help you rank for the search phrase “click here”… not the targeted keyword phrase(s) for the page.