Download from DigitalRiver Windows 7 SP1 different flavors?

I am lost with the ISO's

Source: http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_install/i-do-not-have-windows-7-media-but-i-do-have-my/5ce13741-ac25-4969-ae82-2494726aac1c

Windows 7 Professional x64  with SP1 (bootable)
http://msft.digitalrivercontent.net/win/X17-24281.iso

(EE suggest source)

Source: http://www.heidoc.net/joomla/technology-science/microsoft/14-windows-7-direct-download-links

Windows 7 Professional x64 SP1 U (media refresh) X17-59186.iso

Source: http://technet.microsoft.com/en-us/subscriptions/downloads/default.aspx?pv=36:350#searchTerm=&ProductFamilyId=350&Languages=en&PageSize=10&PageIndex=1&FileId=0

Windows 7 Professional with Service Pack 1 (x64) - DVD (English)

This media refresh includes the installation hotfix described in KB Article 2534111. No other changes have been made to the product.

File Name: en_windows_7_professional_with_sp1_x64_dvd_u_676939.iso
Languages: English
SHA1: 0BCFC54019EA175B1EE51F6D2B207A3D14DD2B58

Which is the difference: X17-24281.iso vs X17-59186.iso vs en_windows_7_professional_with_sp1_x64_dvd_u_676939.iso?

How do I know the MD5, SHA-1 checksums and the ISO file size of the suggest source?

Is the suggest source the U edition?

Last question: I don't want to install Windows Media Player, Windows Media Center, and Windows DVD Maker and IE in one computer

If I have a Windows 7 Professional and Ultimate full Retail (x32 & x64) valid product key and I live in the USA can I download the N edition?

If yes where I can download them safely?

Please provide source Url

Thanks
Rebel