Hi krass - it can be easier to build a bent piece as straight and flat initially and then use the Transform > Deform > Flow (new in MoI v3) function to deform it into the bent position:
http://moi3d.com/3.0/docs/moi_command_reference8.htm#flow

Just at first glance it's not particularly clear to me how that piece you show is supposed to be formed though. Do you possibly have any pictures of the part itself?

- Michael