MySql with Full text search massive use and huge database

Hi,

what i intend to do is to create a web application that needs to work with large capacity of inforamtion (around the 2-3 Terra) most of it in text, so people will have to search inside this huge data storage, and the big problem is let to estimated amount of 30,000 users work in this system in the rang of 10 min which can lead to more then 100-200 conccurent users on the system.
i want very much use mysql with the full text search options which made my life much easiar, and i known the fact and needs of using more then one (even 2 or 3) app server for web but what the hell can i do to minimize the scattering of the database server to minimum computers but still that it will be able to handle the traffic of many users in the same time.
things that i haved thought that may be a problem are:

to devide the database to more then one sever but still dont harm the full text search
to work with more than half terra with one machine, is it good or its better to devide it to more then one and then what to do to connect between them with out too much complications

if you can help me decide or give advices concernig the fulltext search working with large database it will be greate


Jonathan Ben Anat