Bovi, let me propose few tweaks for the installer which I used for some minor mod. Some of them are too late to implement for EB 1.x since no major updates are expected, but maybe you find them useful for EB2 ;)
Code:
[Setup]
; prevent confusing warning about existing directory
DirExistsWarning=no
EnableDirDoesntExistWarning=yes
; keep AppId the same for all installers 
; and they will select previous installation target dir by default
AppId=Europa Barbarorum
; invoke code to guess install directory for users having only one installation
DefaultDirName={code:DefDestDir}

...

{Code}
function DefDestDir(NoArg: String): String;
  var
    Path: String;
begin
  if RegQueryStringValue(HKEY_LOCAL_MACHINE, 
    'SOFTWARE\The Creative Assembly\Rome - Total War - Gold Edition', 'InstallPath', Path) then
    Result := Path
  else if RegQueryStringValue(HKEY_LOCAL_MACHINE,
    'SOFTWARE\The Creative Assembly\Rome - Total War', 'InstallPath', Path) then
    Result := Path
  else
    Result := ExpandConstant('{pf}\Activision\Rome - Total War');
end;

// trying to be smart and warn users against selecting wrong directory
function NextButtonClick(CurPageID: Integer): Boolean;
begin
  if CurPageID = wpSelectDir then
    Result := (FileExists(RemoveBackslashUnlessRoot(WizardDirValue) + '\RomeTW.exe') or
      (MsgBox('The installer cannot find RomeTW.exe in the destination directory. Are you sure you want to use the selected directory?',
         mbConfirmation, MB_YESNO) = IDYES))
  else
    Result := True;
end;
Please replace curly braces around Code with square ones, the forum is too smart trying to find its tags