I know this might sound weird to some but I need answers quickly for what I'm trying to do. How does Google Page Rank evaluate subdomains each with different niches in a domain? Does it consider subdomains as seperate sites from each other when Page Ranking is being considered? What are the differences between a site having multiple subdomains compared to having multiple domains?
Pagerank is a per-page algorithm. That means that Pagerank is assigned based on how many pages are linking to that page. It does not matter whether the page is on a subdomain or not. Do take into account though that getting a good pagerank and ranking a site aren't the same thing AT ALL. Read up on SEO for the rest of your (mostly implied) questions.
total nonsense.....if you have a related term put it in a subfolder on the main site... use subdomains if the terms are not related at all or for administration purposes
How is it TOTAL nonsense. It clearly does work to improve somes sites SEO. I have often seen http://keyword.domain.com popping up on the first page of google for the keyword.
Subdomain or subfolder is the same. Google for careerplanning (I know it's 2 words, but it's the only example I could come up with). #1 careerplanning.about.com #2 www. cthrc .ca/careerplanning/ about.com just ranks higher because they did more SEO on the page. Then google inurl:careerplanning. Both still there. That's because google sees subdomains and subfolders all part of the url. So I would agree that pagerank is determined per page and has nothing to do with sub-anything. You could rank #1 for a keyword with subdomain.subdomain.domain.info/folder/folder/page_bla-bla-keyword.html if you do your on page SEO right.
I refer you to this writeup of Irishwonder: http://www.irishwonder.syndk8.co.uk/2007/03/06/subdomains-or-subfolders-whats-better/ It explains differences between subdomains and subfolders from SEO point of view.