I am sure WMI doesn't have any methods to perform such a task, you can use WMI to display partition information though, I may be wrong.
Meanwhile, I can suggest you to have a look at diskpart utility, it's very easy to use and is supported on Windows 2003 servers.
Akeel is right. If you take a look at the Microsoft WMI "Scriptomatic" or their Technet Script Center, they both give you a large catalog of the things you can do with WMI. In neither case do they talk about creating partitions, but they do give examples for querying the data. Here are some useful links to these toolkits:
Technet Script Center:
Make sure you format the newly created disk using FORMAT <driveletter:>