Hi Brad, first of all sorry for my poor english and apologize me for some mistakes on my written english, i can tell you my personal experience on Windows Server 2008 and IIS7.5
I configure myself my community based on Dolphin 7 after some but reasonable problem and stops on WS2008, IIS7.5 and MYSQL 5.1.
I'm a system manger and developer (best experience on ASP/ASP.NET and less on PHP) but the support of PHP on IIS7.5 for me is very excellent and fast_cgi mode is enabled by default....this boost dolphin application very well but also needed some right hardware resources such as memory and cpu capacity.
My community counts 11.000 members but also 30% -40% is really active. My server machine is a PENTIUM D 1.6 Ghz with 2GB Memory and some burst request grows up cpu usage to 100%
On installation pay attention on Orca Forum that request php_xsl.dll, in my installation doesn't exist but after this the installation is going without problem.
Some other problems at this moment i have, for example after i have changed hostname on dolphin configuration file, all is ok except crop tool for users that before functionally very well.
Now i'm searching a solution for this problem.....