Center the nav in Twitter Bootstrap

Possible duplicate of Modify twitter bootstrap navbar.
I guess this is what you are looking for (copied):

.navbar .nav,
.navbar .nav > li {
  float:none;
  display:inline-block;
  *display:inline; /* ie7 fix */
  *zoom:1; /* hasLayout ie7 trigger */
  vertical-align: top;
}

.navbar-inner {
  text-align:center;
}

As stated in the linked answer, you should make a new class with these properties and add it to the nav div.