I'm not really sure why high PR site wants to link with zero PR site, since I don't have high PR site just yet (so far only PR5), but if I do have, then several considerations when I decide to link to site with zero PR would be : 1. The content is related to my website 2. The website seems created profesionally, not just MFA sites 3. Rich content 4. The owner ask politely FYI, I think the only thing that make sense when high PR website accept my link would be because of reason no 1 and 4, since my website is still new, I don't have a lot of content (which exclude reason no 3) and I'm not sure if my website layout look great for them But the point is, keep trying to request for link exchange, begging them, search in google for the websites that have related content to your site.
Use Keywords with which you would like to be found in search engines and use them often in your pages and link those keywords to your related pages. i.e. If you are selling mp3 players, create an article page that talks about a variety of mp3 players currently in the market. And lets say "cheapest mp3 players" is one of your keywords. Use that keyword in your article and put a link on that keyword pointing to your cheapest mp3 player category products. Again, different search engines interpret the frequency of a keyword differently, I would suggest moderation on the use of the same keyword within a page.
Bold the keyword a couple of times on the page.... you only need to use it once every few paragraphs... that will suffice just fine.