These are available from any Dealer or ebay, craig's list, etc. But they're usually outrageously expensive. Yesterday I saw a couple '99 Owners Manual packs on ebay 1 for current bid of $60 -
http://cgi.ebay.com/ebaymotors/1999-Porsche-Boxster-986-owners-manual-set_W0QQitemZ260212189276QQcmdZViewItem?hash=item2 60212189276 , and 1 for $190! -
http://cgi.ebay.com/ebaymotors/99-Porsche-986-Boxster-Owners-Owners-Manual-Book-Set_W0QQitemZ260211500686QQcmdZViewItem?hash=item2 60211500686
Or, go over to:
www.renntech.org and register, if you're not already. Then send a PM to Loren and see if he can send you a .pdf copy. They used to have it posted there for download, but pulled the earlier years in favor of the later model years, but I bet Loren can get you one.