Ok say if I get a link from a domain from a PR6 page. Then another PR6 on that same website. Does 1 get included or 2? How important is it?
It's still worth something, but not as much as the first one. Generally, you're probably best off sticking to one link per domain.
Sitewide links are helpful, but too many links from the same domain / ip address might not help that much. Stick with one link only, and my advice is to get the one with less outgoing links if possible