@vermaden: I've been checking and indeed it seems that the soon-to-be-shipped Sun xVM Server is what I was waiting for for Solaris 10.
I have no clue. But ive heard that VB is only able to run one VM at a time. Therefore you want to run VB in multi zones, yes?
Yes and not only. Running multiple instances of VB in multiple zones would allow me to solve the problem of the TCP ports. Every VM instance in a zone would have its IP and its ports: two instances of VB running a Windows guest each using, for example, ports 137 to 139, could run without problems and even if every VB would NAT, from the outside there would no problem. Without crossbow and running VMs in the global zone I found no way to solve this problem.
The documentation I read about Xen@OpenSolaris and Sun xVM Server promises to solve this problem. Luckily I'll just wait a couple of months because switching to SXCE or OpenSolaris is not an option here.