Windows Vista is at end of life on 11 April 2017. It is not a good idea to invest in buying a CD for it. You should be considering a newer computer.
https://support.microsoft.com/en-ca/help/13853/windows-lifecycle-fact-sheet
End of support refers to the date when Microsoft no longer provides automatic fixes, updates, or online technical assistance. This is the time to make sure you have the latest available update or service pack installed. Without Microsoft support, you will no longer receive security updates that can help protect your PC from harmful viruses, spyware, and other malicious software that can steal your personal information. For more information go to Microsoft Support Lifecycle.
