PHP can be installed on Windows 2003 and IIS will run it fine. If you are in need of running .NET you will most absolutely have to convert it line by line. Your CSS and you XML will transfer fine from PHP to .NET without any alteration.
My I ask why you are being asked to convert an already working project to a completely different platform?
See...
PHP was designed to run on Linux
.NET was designed to run on Windows
PHP is a "scripted" language
.NET is an "object oriented" language
PHP integrates the code and the markup in a big mashup mess
.NET separates the code from the markup
This is definately not an apples to apples comparison... more like apples to sports cars.
Chase

Visual Studio 2008
ASP.NET 3.5 (Visual Basic)
SQL Server Express
Check out my blog