Hi, Does internal linking structure have something to do with the PR of the site? Does it any any ways influence the SEO of the site?. Please comment.
Ecxcellent internal link structure will enable you to pass PR easier, not to mention aid SEO of the site, which is of course more importnat.
Is there any particular guidelines Google follows, or is it the visibility of links all that matters?
You can refer to the Google Webmaster Guidelines. Text links are the best for internal linking structure.