Downloading these ISO images from Digital River is legal and free of charge. Downloaded ISO images will be of virus and malware free as Digital River is official Download Channel. However you need to purchase a license key to activate Windows 7 after using for 30 days.
Download Windows 7 Integrated SP1 ISO Images
Windows 7 Home Premium x86 SP1 (bootable)
http://msft.digitalrivercontent.net/win/X17-24208.iso
Windows 7 Home Premium x64 SP1 (bootable)
http://msft.digitalrivercontent.net/win/X17-24209.iso
Windows 7 Professional x86 SP1 (bootable)
http://msft.digitalrivercontent.net/win/X17-24280.iso
Windows 7 Professional x64 SP1 (bootable)
http://msft.digitalrivercontent.net/win/X17-24281.iso
Windows 7 Ultimate x86 SP1 (bootable)
http://msft.digitalrivercontent.net/win/X17-24394.iso
Windows 7 Ultimate X64 SP1 (bootable)
http://msft.digitalrivercontent.net/win/X17-24395.iso
After downloading these images, you can burn them to DVD without any burning software from Windows 7 by right clicking on the image.