Several good videos here:
https://www.youtube.com/results?search_query=access+engine+compartment+on+ boxster
Your owner's manual also has the procedure for accessing the engine compartment. It can be kind of intimidating the first time, but it is pretty easy and only takes a few moments once you get used to it.
Here's a download for the 2005 Boxster manual if you don't have a hardcopy:
http://jdmfsm.info/Auto/Other/Porshe/Owners%20Manuals/porsche_boxster_owners_manual_2005.pdf
Page 185 for opening the engine compartment and page 189 for the procedure to check the power steering fluid. NAPA auto parts usually carries The Pentosin CHF 11 S.