If what I think you want to do, yes you can do that. When you install the OS to the SSD, make sure the SSD is the only Hard Drive installed in the system. set the boot order to 1. CD/DVD, 2.SSD Save and exit. assuming everything boots properly, shut down and connect the other HD. As far as the user files-Documents, music. photos- read this tutorial User Folders - Change Default Location
This will enable you to leave the user files on your present but they will appear as though they were on the SSD. That is what most of us with SSDs do.
Also, Bobkn was absolutely correct. Be certain to get an external hard drive. Make frequent images of your OS and keep duplicate copies of user files. Trust me, you will need them at some point. I have 4 externl hard drives, they have more than 1 use and are essential to having a secure computer.
You mentioned a new system. If that is correct your old OS may not work due to different hardware and drivers
. If you want, once you have retrieved all of the information from the old OS, it can be deleted if you like.