numnum - 2:10 am on Jun 30, 2012 (gmt 0)
I don't see a problem. I'm doing this with a static html site (all files have .htm extension). I've installed WP in a /blog folder I created, and all WP files in in that folder. Everything stays separate from the pre-existing site pages. Even if I had installed WP in the root directory, there probably would not have been a problem, since the file extensions are different--as long as the names of the two CSS style sheet files are different.