A PHP plugin for Visual Studio.Net? I'd tend to doubt it. Most PHP developers write in straight text editors and I somehow doubt that PHP support was very high on the .Net developers TODO list, what with them trying to figure out ways to leverage the Evil Empire into internet dominance with dodgy proprietary techonology/licensing schemes/paying Bill everytime I sh*te and all...... <evil laugh>HAHAHAHAHAH!!!!!</evil laugh>.
If it's good syntax highlighting and auto-completion you're after, check out EditPlus. If offers user configurable (ie. you can write your own syntax and completion rules) for PHP, Perl, C (real C🙂, Java, JavaScript, HMTL, SQL, Apache conf, CSS, JSP, and VBScript. C# isn't supported (that I know of) but you can whip your own file up pretty quickly.
geoff
rm -rf /bin/laden
rm -rf /bill/gates
rm -rf /ms/.net