What are the differences between the PG-13 version and the R-Rated version of this movie?
All US versions of this werewolf movie have been cut in order to obtain a PG-13 rating and even the home cinema releases don't feature the R-Rated uncut version that has been released internationally. And for a real horror/action flick this version is the one to get because it's much more violent than the US version and contains several bloody scenes but also sex and nudity. A detailed comparison between both versions with pictures can be found here.
Is there somewhere on the web that I can see some interviews and clips from Skinwalkers?
Yes:YourGeekNews.com has a 10-minute video feature, with exclusive scenes and interviews with the cast (Jason Behr, Sarah Carter, Rhona Mitra) and the crew (Creature Effects Specialist Stan Winston and Director Jim Isaac).