check if your windows 7 iso is authentic +

This is actually quite simple. Go to Microsoft TechNet site and see the details listed under each iso file. If you want to verify your SHA1 key, use the Microsoft File Checksum Integrity Verifier setup installer (KB841290).

For example, the Windows 7 Ultimate DVD has the following information:
File Name: en_windows_7_ultimate_x64_dvd_x15-65922.iso
Date Posted (UTC): 8/6/2009 9:59:56 AM
SHA1: 326327CC2FF9F05379F5058C41BE6BC5E004BAA7
ISO/CRC: 1F1257CA

To install the Microsoft File Checksum Integrity Verifier, all you have to do is add the fciv.exe file to your System32 directory. To display the SHA1 hash of a file, open a command prompt window and run this command:
C:> fciv.exe -sha1 d:/en_windows_7_ultimate_x64_dvd_x15-65922.iso

If you want to verify what build you have installed, open this Registry editor key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion

You will notice the BuildLabEx value.