If you already own a license, the safest way to download it is by logging into your MAGIX account . Your account dashboard typically hosts download links for every version you have previously registered.
If you do not have a pre-existing license, finding a legitimate download for version 9.0 specifically is difficult. Sony Vegas 9.0 Pro Download
This site maintains a version history for VEGAS Pro where older files are stored for users with compatibility issues on newer hardware. If you already own a license, the safest