Hi there,
I think its fairly standard across all Land Rovers.
First of all you need a code. This was supplied on a credit card sized piece of card with the original vehicle. I'l assume its not to hand...
Typically, you can source the code (which is specific to your serial number / radio) from a supplier such as this on eBay:
http://cgi.ebay.com/Landrover-Radio-Code-Decode-Service-4775-Navigation-/380181370976?cmd=ViewItem&pt=UK_Audio_TV_Electronics_In_Car_Entertainment_GPS_In_Car_Audio_Players_PP&hash=item5884935860
Code in hand, you are ready to enter it and unlock the radio.
You only actually need numbered button <1> and the two seek buttons that look like <| and >| .
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When you turn the radio on, you should see it request <CODE>
Press preset button <1>. This should identify character 1 of the code.
Use one of the two tuning buttons (Seek up , or seek down - the ones with arrows going into lines) to move to the right number (0-9).
Press preset button <1> again to lock digit 1 and move onto code digit 2.
Repeat twiddling the upseek and downseek. Press button 1 etc .... until all four codes have been entered.
When you press <1> for the final time, if the code is correct, you'll get a two tone beep to confirm and the radio is unlocked.
If incorrect, you are progressively locked out (in doubling time periods).
Hope this helps.