Bootstrap(fluid-layout) - Align three DIV's in center

Bootstrap(fluid-layout) - Align three DIV's in center

I've following layout in bootstrap- fluid layout
<div class="container">
<div class="span3 offset1"> </div>
<div class="span3"> </div>
<div class="span3"> </div>
</div>
My problem is i want to align all the three spans perfectly center aligned
As i am using fluid layout...in full screen above layout is perfectly
aligned centre as i've applied fixed offset for the first div
But as it gets smaller in width. all the above 3 div's are not being
perfectly aligned in center, as offset is fixed.
I think, here is what happening..... in bootstrap we have 12 colums, all
columns occupying 9 spans..remaining are 3 spans (odd) because of that odd
number i am not able to leave even spans on both sides.....
is there any solution for this?.....