thank you for your answer.
eventually what i did was configuring Vswitch 0 containing VM1 attached to VNIC1 with internet access (through proxy server in my case)
and another vSwitch1 (internal) with no physical nic attached which contains the internal VM2 and VM3 + VM1 with the internet connection.
than on the VM1 installed with microsoft server , i added a second VNIC2 attached to the internal network.
than "Internet Connection Sharing" on the VNIC1.
eventually i also had to configure the Proxy settings for internal VM2+VM3 in the browser settings.
is this an akward configuration?
thanks a lot !
itai