I cannot INSTALL it Zimbra

I keep getting:

Windows Installer error -
This installation package could not be opened. Contact the application vendor to verify that this is a valid Windows Installer package

so, I tried a few things:
1.deleting the file i just downloaded and tried downloading a new one then restart my PC - same result
2.tried modifying registry setting of Win31FileSystem & NtfsDisable8dot3NameCreation to 0 - same result

OS:Windows 7
Dwnloaded file: zdesktop_2_0_b10580_win32 / 3.05MB

What gives? I just want to have a free decent client mail that i can BRAG about.

Please help