I'm looking forward installing a CMS for my sites - most likely Joomla - but apparently Windows hosting doesn't support it. I was wondering what kind of changes I'd have to perform if I changed to Linux. It took me a long time to finally have the PHP form working and I wouldn't want to go all through that again. Aside from that and a Wordpress widget, I don't think I use any other code that would need tweaking.
In a standard linux (apache webserver) hosting environment it should be easier to get a php form and wordpress widget to work without tweaks. Without knowing what you did to make them work, it's difficult to answer your question. I've used hosts such as readyhosting.com that allow php to run on windows servers, but many hosts have better support for php based applications on linux hosting.
Overall, moving to a linux host for easy management of a cms system should outweigh whatever work it took to get your other items working on windows.
Windows hosting is not just for ASP.NET. You can use Apache, PHP, and MySQL very easily here.
This is the platform that the majority of developers use for PHP and MySQL (for example: mysql.com reported that 6-7 out of 10 downloads where for Windows builds, in 2009). And there is no reason why you can't get a Windows VPS, uninstall any control panel that comes with it or disable IIS, and use Apache + PHP + MySQL.
You could also use an all-in-one wamp package that will install this software for you.
There are free packages such as XAMPP and WampServer.
There are also commercial packages such as Wamp Developer, which installs Joomla for you automatically.