IF want a web server very extensible and customizabe, Linux is your choice. Even though microsoft WIN2kAS has many advantages, it´s still the famous "one size fits all"...
For pragrming languages, linux is growing fast and many languages are being ported there "kylix" is a example of that. Windows is a good desktop for my brother, or even my father, but for a wor in progress that is my server I rather use linux, even when I'm not sure of what I´m doing...
Text configurantion is much more efective than point and click