Adding to a database

[Allen May]

I need some reasurance...

I have an existing MySQL database that has basic user information. I am
using it to authenticate users on our web site. I has ID, Password,
FirstName, LastName etc.

We want to add columns at the end of this database for more detail... City,
State, Zip, Phone, etc. I am litle uneasy that I may completely mess up my
existing database if I do this.

Can someone give feedback of A) a better suggestion or B) if doing this will
break my database?

Thanks for any feedback.

-Allen