Your terminology is a little confusing to me. If I'm reading your question correctly you have two SATA HDDs, one is 250GB with XP Pro installed and the other is an 80GB with Vista installed and you want to use the 80GB for storage. What I don't understand is what's stopping you from using the 80GB HDD for storage right now. Set your BIOS to boot from the 250GB drive and the 80Gb will appear as the next available drive letter. Vista will take up some of the 80GB but will not interfere with using the drive for storage. The alternative is to re-format the 80GB HDD and lose the Vista installation.