Can I install 10.9 over 10.8 and maintain windows xp boot camp functionality?
When I recently installed OS X 10.9.1 over 10.8.5 on my mid-2010 Mac Mini running Windows XP in Boot Camp, XP continued to work fine in Boot Camp.  I don't run Parallels, and I don't have your exact configuration, so I can't guarantee results.  Additional information: I had originally installed XP in Boot Camp when my Mac was running Snow Leopard, and I subsequently upgraded to Lion, then Mountain Lion, then Mavericks.  Microsoft is stopping security patches for XP in April 2014, so if you use XP on the network, you may want to install a newer version of Windows.