Now Pre-Registration of .MX domain names is open for everyone without organization or location restrictions. But the catch is you need to already own a .com.mx domain name as of now.
Godaddy, a popular domain name registrar sent an email that persons who owned a .com.mx prior to March 1, 2009 can apply for the .MX domain names. However, if you owned a .com.mx prior to March 1, you can transfer domain to them and then pre-register for the .mx. domain at Go Daddy.
Remember if you do not own a .com.mx, you do not qualify for the pre-registration period. Pre-Registration period ends July 31, 2009 and after that open public registration begins September 1, 2009.
If you have anything remotely to do with Mexico, its a good idea to get your own .MX domain name. Also it is a good idea to convert your .com.mx domain name to .mx which is much better. You can visit nic.mx and registry.mx (non-english) for more information.