Step 1: What you'll need
All you need is:
A Mac (this guide is for 10.4 but im sure it would be very similar on 10.5)
And XBOX 360 (duh)
A wireless network to connect your Mac to (your own)
The ethernet cable that came with the XBOX
AT THIS POINT LOOK UP HOW TO SET A STATIC IP ADDRESS AND DO IT.
Step 2: To begin
2. Make sure location is set to "Automatic" and show is set to "Built-in Ethernet."
3. Now where is says "Configure IPv4," select Manually.
4. Enter in 10.0.0.1 as the IP Address.
5. Enter in 255.255.255.0 as your Subnet Mask.
Step 3: Now
Step 4: Back to System Preferences
2. Click on the "Internet" tab.
3. Make sure that on the drop down menu Airport is selected.
4. Click on the box next to "Built-in Ethernet" and hit "Start" at the top.
5. Go ahead and connect your Mac to your XBOX via the ethernet cable.
Step 5: Now on your XBOX
2. Go down to "Network Settings."
3. Now select "Edit Settings."
4. Select your IP settings and choose "Manual."
5. Now enter 10.0.0.2 as your IP Address, 255.255.255.0 as your Subnet Mask, and 10.0.0.1 as your Gateway and hit done.
6. Go ahead and test it right now, it will fail.
7. Now go back to edit network settings and select your DNS settings this time and once again choose "Manual."
8. Enter in the IP Address that is on the bottom of your router as your Primary DNS Server (mine would be 192.168.1.1).
9. Now get out that IP address that you obtained earlier from your router and enter it in as your Secondary DNS Server.
10. Select done and test your connection.