Network Over Mains acting as a bridge

I have a VirginMedia modem that supplies my connection to the
Internet. I connect an Ethernet cable to a Sitecom wireless router
(this has a 4-port hub), which I have a laptop connecting to the
router wirelessly and a XBox 360 connecting wired. Both the laptop and
the XBox connect fine to the Internet using the router's DHCP and
through to the cable modem from Virgin Media. I'm happy with this set
up but this is restrictive to the length of cable or the wireless
signal so I want to expand using wires.

I have purchased a networking over mains kit so that I can connect a
PC from my back room to the front of the house by connecting 1 mains
Ethernet plug to the Sitecom router and the other mains Ethernet plug
to the PC. This works fine and connects to the Internet because it is
just another client connecting to my Sitecom router through to the
VirginMedia cable modem.

What I now want to do is connect several PCs in my back room so was
thinking of getting a 4-port hub. In my thinking I can keep the
networking over mains plug in the Sitecom router but instead of
connecting the other networking mains plug to a single PC, I would
connect it to a hub. From there, I would connect several PCs to the
Hub. Thus my question is, can you use networking over mains to act as
a bridge between the Sitecom router and the hub to not only connect to
each other but act as an internet network and also allow any PC
connected to the hub to have Internet connection. The Internet
connection from a PC connected to the hub would take a path of:
- The PC is connected to the hub via an Ethernet cable to a spare
port.
- The Hub (using the uplink port) is connected via an Ethernet cable
to networking over mains plug
- The other networking over mains plug is connected via an Ethernet
cable to the Sitecom router.
- The Sitecom router is connected via an Ethernet cable to the Virgin
Media cable modem.

All PCs are using Win XP Pro and would be all be part of the same
workgroup to enable file sharing.

Is this addition of the 4-port hub possible?

Any help will be greatly appreaciated.

Steve