There are two sets of files there: oc-db.gz is a gzipped text file containing the database contents. The format should be self-evident, but isn't stable, and is likely to change in the future.
The remaining files are in rss format. This is probably the most common format for exporting weblog pages (the specification is on the UserLand site). Although the format is XML-based, there are plenty of tools around for working with it; for a start, see the Mother of Perl tutorial, which includes a simple perl script for rss-to-html conversion. There are 2 versions of the O.C. rdf files - one with, one without, all the details. The idea is that you adapt the appearance to fit in with your own pages, though.
There's no regular schedule for updating the files: they get updated locally whenever a new addition is made to the news page or the database. If you want to import them, one download a day should be plenty (unless open hardware really takes off ;-)
Current feeds are: