I want to make a custom rebel helmet but I dont know how to make the curve/dome part here is an
image
this is not the helmet i am making, only a reference to show the dome that I mean.

Well one thing's for sure, you'll want to start with a sphere primitive

well in this bender tutorial https://www.youtube.com/watch?v=GfmD9XMrdYc he uses a grid to make the curves without a sphere is there a way to do this in xsi

Yeah probably by subdividing and tracing the outline of the helmet, but using a sphere like Marth said is much easier. Just extrude the rectangular polys from the sphere to add the comm box.

He doesn't use a grid in the video, it's a quarter sphere with a mirror modifier. Everything seen in that video can be easily reproduced in XSI.

http://virtuverse.wikia.com/wiki/XSI_-_ ... l_Modeling