I think you're talking about an TLD, correct? IDN is about domains with non-alphanumeric characters.
If you want a 2 letter TLD, start your own country first, or buy the rights of a small country. For instance, a Canadian entrepreneur bought the rights to .tv (Tuvalu) for $50 million (for 10 years).
For other gTLDs, perhaps visit
http://gnso.icann.org/reference-documents.htm
Other considerations :
- buy a short domain with an existing extension (like to.be), and start selling subdomains (eg. rich.to.be)
or
- develop a browser plugin which maps your extension to a subdomain behind the scenes. Of course you'll need to be able to spread your plugin to all browsers
or
- create your own root server (don't know wether this is really possible)
