Yes, you can have 2 hard drives in one PC.
Yes, you can have 2 different OS'es in one PC.
- you can run only one OS at the same time (to switch: shut down and reboot)
- you can't use programs installed in OS 1 when using OS 2 (so you can't use your XP programs while using Vista and you can't use your Vista programs while using XP)
You use Virtual PC. But that can be done on one hard disk just as well. And it needs a fresh install of the OS and all applications on that virtual machine. But than you can easily switch between the 2 OS'es.
So what you want is not possible. So no step-by-step.
Even a step-by-step on just installing the old drive and using it as storage isn't possible without knowing details like SATA and ATA of your machines.
I have a New Acer AX3200 with Vista Home Premium but I would like to connect my old hard drive which has XP Media Center and all my softwares installed with the Acer. Will there be any problems because the drives have two OS installed in them? Can someone PLEASE help me on a step to step process on how to go about with having my old drive installed in my new PC? Thanks.