How to install the AMD64 updates:
When released, these updates required an AMD Athlon 64 processor and Windows Professional x64 Retail Version to be installed, otherwise the updates could not be applied. However, it has since been discovered that is possible to apply these updates to FarCry on a system with a 64-bit CPU/32-bit OS (Win XP) and even a 32-bit CPU/32-bit OS (Win XP).
STEP BY STEP GUIDE:
1. Download the AMD64 Upgrade (486MB) and AMD64 Exclusive Content Update (422MB).
2. Before installing the files, make sure that you have the Windows Installer 3.1 package on your system. If you keep your system regularly updated via Windows Update it should already be installed, alternatively download and install the redistributable from Microsoft.
3. Extract each upgrade to a separate directory, e.g. C:\FC64U for the upgrade and C:\FC64ECU for the exclusive content.
4. Select the START menu and then Run... and in turn, browse to the directory to where the update/content executable was extracted, but don't run it yet. It doesn't matter in which order this is done.
5. So, for the upgrade, you would select C:\FC64U and select the farcry_amd64upgrade_us_uk.exe file and press Open, but do not press OK yet. Add /a to the line present in the Run... command and then press OK, i.e. you should have the following in the Run... command before pressing OK:
"C:\FC64U\farcry_amd64upgrade_us_uk.exe" /a
Press OK and the extraction process will now begin.
6. Do the same thing for the exclusive content update -- so, using the directories listed above, the following path would be indicated in the Run... command:
"C:\FC64ECU\farcry_amd64_ecu.exe" /a
Press OK and wait for the extraction to complete.
7. While extracting, both processes may appear to hang/stall, but you should notice that the HDD will be very active during the extraction and it will take a couple of minutes for each one to complete.
8. After both extraction processes have completed, go to each directory (again, it doesn't matter in which order this done) where the files have been extracted and then select all files and folders within ...\Far Cry folder and copy them over to your Far Cry install directory.
So, for the upgrade you would navigate to
C:\FC64U\Program Files\Ubisoft\Crytek\Far Cry
and for the exclusive content update you would navigate to
C:\FC64ECU\Program Files\Ubisoft\Crytek\Far Cry
and in turn select all the files within the ...\Far Cry directory and copy them over to your Far Cry game install directory, e.g.
C:\Program Files\CryTek\Far Cry
Ignore any warnings and select yes, overwrite all if prompted.
9. When done, run the game. If it has worked you will see an AMD64 animated video before the Far Cry menu appears.
What is FarCry 64-bit content?
The AMD64 Enhanced Content Update was released as an optional download in May 2005 to showcase improvements in FarCry made possible by AMD's 64-bit architecture.
These AMD 64 update additions include:
* Optimised and refactored code to take advantage of 64 bit architecture.
* Two AMD64 exclusive multiplayer maps – MP_Stronghold and MP_Gorge
* Added Offset bump mapping support.
* Added higher resolution textures and objects.
* Increased some viewing distances
* Updated the Pier level with new content
Thanks to Guinny at the OcUK forums who originally posted this there. He in turn thanks unstrain1969 from the Far Cry forums for originally getting this to work.