In the very many modeling functions of XSI, is there a to curve a cube or something?

There is a way to curve a cube, yes.
But one-click function? No.

A short tut in case you don't know how to curve the edge of a box I made for Deathrow.

Advisory: Extremely Simple! Oh, yeah, this was in Max, but it's basically the same in XSI.

Step 1:
Create a box.




Step 2:
Move first set of middle segments steeply outward.




Step 3:
Move next set of middle segments less steeply outward




Step 4:
Repeat step 3 until you get to your last point (or last set of middle segments), which should be moved outward least steeply.

do you have to have all those sections?

Sub divisions? Yes.

But after you make your curve as shown by Taivyx you can select the model and do a filter polygons which will remove the extra sections from the top and bottom and leave the curved front

Thanks yall'! This should be a sticky.