Yes filenames will affect page rank if you change that from filename.html to filename.htm or any other file.
Does page rank increase by having each page as http://www.xxxx.com/contact/ and /portfolio/ rather than ?page=contact etc?
Page rank is related to the number of links pointing at your site. You may get higher rankings in the search engines from using filenames with the keywords in them but this is nothing to do with pagerank.
IMO using keywords in the filename does not help with rankings anymore. At least not enough to go crazy with it? Anyone else have an opinion on this.
Don't give much importance to PR and you can use keywords in filenames and directory structure, it will help in getting higher rankings in SERPS (with ofcourse, all other methods)
Yeah, a lot of people talk about page rank (meaning their rankings) and get PR and page rank confused. URL structure has absolutely no bearing on your google PR number in any way shape or form. That is 100% determined by incoming links. Anyone who says that PR can be effected by anything other than links is a moron. Unless you're talking about spreading PR. That depends on your internal link structure as well as incoming links. But your home pages PR is 100% incoming links and thats it.