I work for a travel agency, they have a website, from here they want to give the option to their travels to create their own subdomain with a wordpress blog inside.
More or less what the webpage http://wordpress.com/ offers its users.
What do I need? And plz links.
A solution might be to use "Wordpress MU", the "multi-user" version of wordpress ; install it on some webserver, and configure it ; and it should do what you want
Actually, like said on its website (quoting) :
WordPress MU, or multi-user, is designed to do exactly that. It is most famously used for WordPress.com where it serves tens of millions of hits on millions of blogs each day.
So, this should be quite OK for your needs ;-)
For more informations, you can take a look at its readme, which describe how to install and configure and all that.