PR is a function of who links to you and what their
PR is. The
PR of any page is usually one less than the highest
PR linking into that page, at least that's been my observation. So the only way to raise the
PR on your inner pages is to get some links to those specific pages from higher
PR pages.
Personally, I think it's not where the focus should be.
PR is not all that important. More important is how you're listed in the Search Engines. HOW people link to you is just as important, if not more so, than the
PR. For my business, a link from any page, no matter its
PR, about "Web Application Templating Systems", with a link to me using that phrase as the anchor text, is much more valuable than someone who simply drops a link to me with no explanation, using my url as the anchor text, from a blog about pet cats.
Content is also very important, as has been stated over and over. Adding content to your site would be time better spent than trying to get higher
PR on your inner pages.
But that's just my two cents and I'm sure other people will add theirs or argue with me.