New to CF... just a few questions...

(1) Is there a simple way to output server configurations (like phpinfo() with php)?
Yes, <cfdump var="#server#">. But you will get a much shorter summary than with PHPinfo.

(2) What file extensions are parsed by coldfusion by default? (like, in php, I can parse .php, .php4, .php5 by default)
cfm, cfml, cfc, cfswf, cfr, jsp, jws

(3) I am looking for a small snippet of code that will output the root directories subdir and files
Save and run the following code as the file listDir.cfm in the directory that you wish to list.

<cfdirectory directory="#getDirectoryFromPath(expandPath('*.*'))#" name="dir" action="LIST" recurse="yes">
<cfdump var="#dir#">

It works for any arbitrary directory. However, be aware that setting the recurse attribute to "yes" instructs Coldfusion to look into directories within directories, directories within directories within directories, and so on. That could take long.

I have saved the best for last. You can use Sean Corfield's scripting tag to run your PHP code directly in Coldfusion. But then, you will need Coldfusion 8, which runs on Java 6.