Can Kavaklıoğlu's questions

We have several of standard non-managed 3com switches in a network. I thought switches were supposed to only send packages between peers of a connection.

However it appears network sniffing software running on a computer attached to one any one of the switches is able to detect traffic (ie youtube video streaming, web pages) of other host computers attached to other switches on the network.

Is this even possible or is the network thoroughly broken?

I am using a loop device disk setup (not lvm) for Xen Debian (squeeze) guest systems on my Debian (squeeze) host system.

I searched for a way of extending guest system disk size. I came accross simple dd commands and nasty mkfs commands.

I wonder if there is a magic xen-tools command set to help me out on Debian systems? Or a simple set of tested dd & mkfs command set for this non-lvm case?

Thanks.