NAT issues with Wireless router, Macbook and Xbox

Hi everybody! This is my first post, so go easy on me
I've had my macbook for nearly 2 years now (ish) but I'm still a virtual nooob when it comes to anything technical :?

Background:
Ok, so basically there's a problem that seems endemic to Xbox Live users in the UK, and on my provider O2 especially, and that's that the 'NAT type' is set to strict. Which seems to mean you find it EXTREMELY hard to find and connect to multiplayer games. Apparently this NAT type can be changed to moderate (connect to most multiplayer games) or open (unrestricted, connect to all).

Using the power of Google I've found a guy who had exactly the same issue and found a solution (http://www.avforums.com/forums/netwo...ss-router.html).

I've got two key problems here, a) I barely understand a word of this, and b) it's in Windows. :?
My questions are this:
1) Could somebody please translate this into Mac (so to speak)?
2) And break it down into bite-size, noob friendly, portions?
3) Even the bit about setting the xbox a fixed IP address and setting up uPnP I'm not sure about!

In case it helps my specs are:
Macbook: 2.4Ghz Intel Core 2 Duo, 2Gb Ram
Thomson/O2 Wireless Box II
Xbox 360 60Gb with WiFi adaptor

Please help.

Thanks,
FJ.