- extract the downloaded file, you will find a file named "data"
- open up your main Rome - Total War folder
- click and drag the data folder you extracted into the file named "PI"
- when asked to overwrite files, select 'Yes to All'
- open the PI folder and run campaign_map_reset (double-click it, a screen will pop up for just a second
if you do not have the campaign_map_reset program, then open up PI/data/world/maps/base and delete map.rwm, and then do the same in PI/data/world/maps/campaign/greek
One other thing, please make sure that the shortcut you use for PI has the following listed at the end of its shortcut path: -show_err -mod:PI -nm
Also, I strongly suggest that you disable the auto-save function to try and avoid corrupted save-game files. To do this, open prefences.txt inside the PI/preferences folder, find the line AUTO_SAVE: and change TRUE to FALSE.
That's all, the patch is now installed. I do not believe that it is save game compatible.