Scripting WMI with PowerShell is far simpler than with using the above mentioned API.

To get instances of a particular WMI class - just use get-wmiobject specifying class and (where needed) the namespace. For example:

PS C:\Documents ad Settings\LeeT> get-wmiobject win32_share | ft -auto

Name   Path                               Description          
----   ----                               -----------          
E$     E:\                                Default share        
IPC$                                      Remote IPC           
D$     D:\                                Default share        
print$ C:\WINDOWS\system32\spool\drivers  Printer Drivers      
phaser Xerox Phaser 8560N PS,LocalsplOnly Xerox Phaser 8560N PS
ADMIN$ C:\WINDOWS                         Remote Admin         
C$     C:\                                Default share