How do I search someone on Hotmail to see if they have an email?
To search the person or the windows live profile that owns the hotmail id :
If the profile is not limited to private, you can search it by email id, first-last name, work, loacation, education, gender etc.
To search if an email id exists or not : http://www.verifyemailaddress.org
Sorry, to correct myself: You can try to guess their email address and see if it's valid. As for actually searching your only option is to login at Live.com, click on "Add friends" and search for their name.
The easiest option is something like Verify Email.
Or you can do the same thing within a command line or Terminal window as described here.
Just to clarify, you are trying to determine if a particular person has an existing Hotmail email account?