I have a client that has an existing site built in ASP and they are asking for a blog. I prefer using Wordpress and installing it manually on their server. My question is whether or not Wordpress can be installed on a server that uses ASP. I have no idea if PHP and MySQL can be on the same server as ASP. Does anyone else know?
You can run PHP as a filter on ISS, although I can’t help you with exact instructions on how to get that set up.
One caveat, last time I ran PHP on IIS (which, tbh, was about 5~6 years ago), it ran horribly (even with an extremely low load), and would irrevocably crash IIS every two weeks or so. I do believe that the combo has gotten a lot more stable since then though.
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Oh yeah, MySQL will run fine on Windows 
As long as the server is properly configured, php/mysql/asp/asp.NET can all peacefully co-exist on the same server and run well. I’ve used a windows host for years that supports such configurations.
Answer: YES! That is the beauty of Windows. You can run ASP, ASP.NET, and PHP side by side without issue. Windows 2008 R2 has great improvements over Windows 2003 in regards to PHP on Windows. Hope this helps. Let me know if you have any specific questions as I’ve dealt with these types of configurations for many years!