Problem with checking the Windows version from Inno Setup - inno-setup

Question

My program installs a driver, which has different versions compiled for XP, Win2003, Vista/Win2008, and Win7. I use pascal functions to check which is the OS, and install the corresponding DLL.
On some users' systems no DLL is installed, which means all the functions have returned false. This should not happen so long as the OS's major version is 5 or 6.
Can anyone tell me if there is something wrong with the code I use?
[Code]
function UseDriverForWindows7(): Boolean;
var
Version: TWindowsVersion;
begin
GetWindowsVersionEx(Version);
// Windows 7 version is 6.1 (workstation)
if (Version.Major = 6) and
(Version.Minor = 1) and
(Version.ProductType = VER_NT_WORKSTATION)
then
Result := True
else
Result := False;
end;
function UseDriverForWindowsVistaAndWindows2008(): Boolean;
var
Version: TWindowsVersion;
begin
GetWindowsVersionEx(Version);
// Anything with major version 6 where we won't use Windows 7 driver
if (Version.Major = 6) and
(not UseDriverForWindows7)
then
Result := True
else
Result := False;
end;
function UseDriverForWindows2003(): Boolean;
var
Version: TWindowsVersion;
begin
GetWindowsVersionEx(Version);
// Windows 2003 version is 5.2 (server)
if (Version.Major = 5) and
(Version.Minor = 2) and
(Version.ProductType <> VER_NT_WORKSTATION)
then
Result := True
else
Result := False;
end;
function UseDriverForWindowsXP(): Boolean;
var
Version: TWindowsVersion;
begin
GetWindowsVersionEx(Version);
// Anything with major version 5 where we won't use Windows 2003 driver
if (Version.Major = 5) and
(not UseDriverForWindows2003)
then
Result := True
else
Result := False;
end;
[Files]
Source: "mydrv-xp-x86.dll"; DestDir: {app}; DestName: mydrv.dll; Check: not IsWin64 and UseDriverForWindowsXP; Flags: ignoreversion
Source: "mydrv-2003-x86.dll"; DestDir: {app}; DestName: mydrv.dll; Check: not IsWin64 and UseDriverForWindows2003; Flags: ignoreversion
Source: "mydrv-vista-x86.dll"; DestDir: {app}; DestName: mydrv.dll; Check: not IsWin64 and UseDriverForWindowsVistaAndWindows2008; Flags: ignoreversion
Source: "mydrv-win7-x86.dll"; DestDir: {app}; DestName: mydrv.dll; Check: not IsWin64 and UseDriverForWindows7; Flags: ignoreversion
Source: "mydrv-xp-x64.dll"; DestDir: {app}; DestName: mydrv.dll; Check: IsWin64 and UseDriverForWindows2003; Flags: ignoreversion
Source: "mydrv-vista-x64.dll"; DestDir: {app}; DestName: mydrv.dll; Check: IsWin64 and UseDriverForWindowsVistaAndWindows2008; Flags: ignoreversion
Source: "mydrv-win7-x64.dll"; DestDir: {app}; DestName: mydrv.dll; Check: IsWin64 and UseDriverForWindows7; Flags: ignoreversion

Answer 1

You should use the common parameters MinVersion and OnlyBelowVersion in conjunction with the function IsWin64.
Update
To distinguish between workstation and server versions you can use the GetWindowsVersionEx function which is integrated in Inno Setup.