The only ISO available on the net are from torrent sites. If you need an untouched ISO that is free from 'cracks' or virus then you have to create one yourself from the original files that are not in ISO format yet. There are three files that you need actually. There's an *.exe file plus the two *.wim files:
For x86 (32-bit) version
http://msft-dnl.digitalrivercontent.net/msoffice/pub/X14-63452/X14-63452.exe
http://msft-dnl.digitalrivercontent.net/msvista/pub/msshus/vista32/boot.wim
http://msft-dnl.digitalrivercontent.net/msvista/pub/msshus/vista32/install.wim
For x64 (64-bit) version
http://msft-dnl.digitalrivercontent.net/msoffice/pub/X14-63453/X14-63453.exe
http://msft-dnl.digitalrivercontent.net/msvista/pub/msshus/vista64/boot.wim
http://msft-dnl.digitalrivercontent.net/msvista/pub/msshus/vista64/install.wim
Those files are genuine, clean and legal to copy provided you own a valid Vista license. They can be used to install any Windows Vista edition (Starter, Home Basic, Home Premium, Business or Ultimate). It is the activation key that determines which Vista edition will be installed.
If you want to make an ISO image, Run the *.exe (either the x14-63452 for 32-bit or x14-63453 for 64-bit, whichever applies in your case). Wait for the Windows Vista system files to unpack to a new folder called Vista. Cancel the Vista setup process when you get to the installation menu. Let's assume the setup files have been unpacked to "C:\Vista\". If they're in a different folder, just replace it in the following steps:
1. To create an iso image, download this:
http://www.sevenforums.com/attachments/tutorials/32382d1256189124-make-bootable-iso-student-d-l-oscdimg.zip
If you're creating a 64 bit iso image (and only if doing so), you'll need this file:
http://www.mydigitallife.info/wp-content/uploads/2008/01/etfsboot.com
Copy that to "C:\Vista\boot\" or wherever the Vista\boot folder is located.
You can begin the iso creation by opening an elevated Command Prompt by right clicking on Command Prompt and 'Run as admin'. Enter the command:
oscdimg –bC:\Vista\boot\etfsboot.com -h -lVISTA_EN_DVD -m -u2 C:\Vista\ C:\windows_vista_with_sp1_dvd.iso
All should be typed in one line before you press Enter.
2. After creation of the ISO, burn the ISO to a DVD using this:
http://www.imgburn.com/
You might need to download drivers from the computer manufacturer's website if you have hardware that are not automatically detected by Windows Vista after running Windows Update.