Found a script online and tweaked it a bit. Figure others would like it to

[CustomMessages]
dotnetmissing=This application requires Microsoft Framework 4.0 which is not yet installed on this computer. Would you like to download it now?


function InitializeSetup(): Boolean;
var
ErrorCode: Integer;
netFrameWorkInstalled : Boolean;
isInstalled: Cardinal;
begin
result := true;

// Check for the .Net 4.0 framework
isInstalled := 0;
netFrameworkInstalled := RegQueryDWordValue(HKLM, 'SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\client', 'Install', isInstalled);
if ((netFrameworkInstalled) and (isInstalled <> 1)) then netFrameworkInstalled := false;




if netFrameworkInstalled = false then
begin
if (MsgBox(ExpandConstant('{cm:dotnetmissing}'),
mbConfirmation, MB_YESNO) = idYes) then
begin
ShellExec('open',
'http://www.microsoft.com/downloads/details.aspx?familyid=9CFB2D51-5FF4-4491-B0E5-B386F32C0992&displaylang=en',
'','',SW_SHOWNORMAL,ewNoWait,ErrorCode);
end;
result := false;
end;

end;