I am looking at Virgins new 30Mb service. As I understand it, it comes with a modem/router/wireless, not just a simple modem as before.

My question is, can I simply use my Vigor 2110n plugged into one of the ports on the new modem router and carry on as before?

How do IP addresses get assigned if this is the case? Do I need to stop the Vigor assigning addresses and let the new Virgin box do it? Or can I simply let the Vigor do everything and just use the new Virgin box as a "modem"? I also will want to continue using the Vigor for wireless, so won't be using that component of the Virgin box either. Just wish I understood more about networking rather than let boxes do the work for me!

Right now, the superhub is annoying, you can't use it as a modem so the only way to get the router to have direct internet access is to connect its WAN port to the SuperHub with a LAN IP (fixed) and use that as the DMZ address on the superhub.
Also the superhub has some DoS defense of it's own that tends to break things (in my experience) - you'll need to go to the Advanced settings > Content Filtering > Services and disable things like IP Flood Detection & Port Scan Detection, probably worth disabling stuff that won't be used like Firewall Features and enable the VPN passthrough options.

I have read that they'll be making a new firmware in a month or two that'll add modem mode so none of that setup will be needed.