There is no such thing as a combined cable modem/router on Virgin.
You can only use the CableModem supplied by VM and it only offers a single Ethernet port.
If you have already ordered the VM wireless router, then I would stick with that, otherwise, any 'Cable' or 'Broadband' router will do. Wireless speed will only be increase using an N router if you also upgrade the wireless adapter, but don't forget you only have a 10Mb connection to share, so a good G or G+ router should be able to max out the modem.
---------- Post added at 17:25 ---------- Previous post was at 17:25 ----------
<Must type quicker>