adding another connection

[#1]

I've got the 'BT 2wire' router from PlusNet which I just use with the yellow (ethernet??) cable and all is well connection wise. Soon I'll be adding another Dell PC is a fairly distant part of the house (through what was once an outside wall, so bricks & mortar rather than plasterboard) and I'm wondering how best to connect it.
The Dell spec says:
Communications 
Network adapter (standard)
10/100/1000 Ethernet LAN on system board

Wireless options
Internal Wi-Fi (802.11g)
Bluetooth®  2.0 wireless technology with Media Card Reader
If it's got internal Wi-Fi would it work through a couple of walls, or can I buy a huge long version of my yellow cable and just plug it in?

[#2]

The huge long version of the yellow cable is the best bet for quality. Might be worth hanging fire though to see what the experience is like on WiFi first though.

[#3]

Hard wiring with your yellow cable is always best (you can make up your own).
Wireless will give a much lower connection speed but unless you are transferring large files between PCs that will be less of a problem.
You could also make use of the house mains electric wiring (NOT by stuffing your yellow cable into the nearest 13 amp socket I hasten to add). There is kit available as others will describe in detail.

[#4]

Cables don't have to be yellow, there's a wide selection of colours. 
Anything up to 100 metres will work fine and can be purchased in various lengths for a few pounds complete with RJ45 connectors on. Normally called "patch leads".
Longer ones tend to be grey.

[#5]

"PCArena - 30 metre Network Ethernet Cable RJ45 PC XBox 30m - PCArena PC Parts"
Does this sound like the correct thing (it's grey  ::)) or is it just for an xbox?

[#6]

sounds good, is that long enough?  wifi through two double brick wall probably wont work