Ok, in that case you probably ought to have a look at:
http://www.netgear.co.uk/wireless_fi...ter_wgr614.php
Then have a look at the firmware version (probably on a sticker underneath somewhere) and download the manual from one of the pages linked from here:
http://kbserver.netgear.com/products/WGR614.asp
You should be able to get information from the manual about port forwarding, if it doesn't make much sense try having a look here:
http://portforward.com/
Where you should be able to find your device, and some half decent instructions on how to get it set up.
I don't know if Virgin will have changed the username and password, if not the default ones will be listed in the instruction manual.
You should set up the wireless security (unless you're not using wireless, in which case turn the wireless off) and change the admin password as well whilst you're poking around.
If you can't make head or tail of any of the above post back with a version number (if there is one) and I'm sure someone can help you through it.