Yesterday I talked about vs.php but you don't need extra components to edit php scripts in the VS.Net IDE....
Copy usertype.dat to your Visual Studio IDE directory (Default install should be C:\Program Files\Microsoft Visual Studio .NET (2003)\Common7\IDE). usertype.dat contains PHP specific keywords.
Import php_edit***.reg (*** = your version) into the registry. All it does is create a .php extension entry, and maps that extension to the C/C++ syntax highlighter/editor.
You get:
= Syntax Highlighting
= Code Folding
Get it here