John1234, I'm sorry to say you must learn to walk before you try to run.
First, the HDR-FOX T2 is a FreeviewHD+ recorder. The HD-FOX T2 is a FreeviewHD+
receiver with no internal hard disk drive, but which can have a limited recording function added by fitting an external USB hard drive. More details
HERE (click).
Your writings suggest you have installed custom firmware and the portal-xtra1 custom package, and as you do not seem to have an Internet connection we come to the assumption you have done so using the USB route. Is this in fact correct? I have to say that at this stage I really don't think you should be fiddling with any custom firmware/software, get the basics established first. The custom firmware will not help you overcome your networking difficulties.
Now what's this about your TV? What you have written suggests to me you are using your computer monitor as the display for your HDR-FOX, or your TV as your computer monitor. That is certainly a way to add live TV capability to a computer monitor, presuming it can accept a composite, SCART, or HDMI input. However, the "usual" configuration around here is to have the HD/HDR-FOX displaying on the TV while we also fiddle around using the PC (with its own display!). Not that that necessarily matters.
I interpret you enquiry as wanting help to get your HDR-FOX connected to your home network and the Internet. The only alternative I can think of is that you want to get a point-to-point network connection going between your PC and your HDR-FOX purely so you can access the web interface for the custom firmware - but like I said let's not go there yet. Connecting directly between the PC and the Humax is more complicated because there is no router in the middle to allocate networking settings.
Presuming the former, you do not connect the HDR-FOX to your PC by Ethernet. You need to connect the HDR-FOX to your network router - either by cable or using a WiFi USB dongle
(details HERE - click). Once you have done that, with "DHCP" in the Internet Setting options you have already found, the router will allocate the appropriate IP address, mask, etc settings and you will have network access on the HDR-FOX. Then you should be able to press the "TV Portal" button on the handset and get access to iPlayer etc - "out of the box", very much the way it says to do it in the manual. That will complete the first step.
Before you then consider moving on to the custom firmware, I think we would like to discuss with you what you think it will do for you and what you want to get out of it.