Check out this website http://www.volvoxc.com or www.volvospeed.com or www.swedespeed.com The flush is pretty easy; if the xc90 is similar to the xc70 you use a hex key to drain the radiator. iPd is the place to get good parts, as well as fcpgroton. Good luck getting the flush done.
www.matthewsvolvosite.com is probably the best DIY board there is. Very friendly and informative. Some of the other sites lean a lot more towards performance and upgrades as opposed to regular maintenance/repair items.
