I've installed NetBSD in Dom0, and two Linux and one Windows in DomU.

  I've two @IP on the Dom0, bge0 10.10.0.2, and bge1 192.168.0.2.

  Xen create a new interface, virbr0 192.168.122.1

  My problem is :

  How can I put an address IP for the 3 DomU in the
  192.168.0.X range ?


You need to configure IP addresses of domU in the domU.  Then, you need
to arrange networking so that this works.  For your case, probably you
should create a bridge (see bridge(4) for more) and add bge1 to it via
brconfig(8) and then also the xvif*.1 interfaces, probably via the xen
domU startup scripts.