Or do you have to do SEO (backlinking and so forth) for each individual page?
Yes, internal linking does distribute Pagerank, the issue is it divided up just the same as with outbound links, so if you have 5 internal links and 5 out bound links on one web page your passing on in theory only 1\10 of the possible value you can.
Now, if Pagerank is divided up different via internal links and out bound links is something only the Google engineers would know and keep secret to prevent abuse. You best bet is to build backlinks to all your web pages, using proper anchor text to help your SERPs as well.
Do you own SEO on each page of your website and you should be able to see better results. If you need some tutorial on SEO, get them for free below :
SEO TUTORIAL PAGE:
http://www.toliveonline.com/SEO/Search%20Engine%20Optimization.htm