Don't run anything else.
You need to install the OS twice. It will create a dual-boot for you... Each time you turn your machine on, it will ask you which OS you want to launch.
The best is first to split your HD in 2 partitions (example: C and D) or to run 2 hard drives. Ask someone who knows a lot about computers to help if you are not sure how to do this.
You install an OS on each. So then you can run those games, graphic apps, internet etc.. on one OS, and have a CLEAN and tweaked OS for your music.
Hell, I actually have 8 different partitions (!) because i set different cluster size for partitions with OS+programs than paritions with large audio files. That's a bit stretching it, but it allows me to grasp at once what need ot be backed-up, and I am not worried if the OS partition fails.. I just wipe it out and re-install without having to backup the rest (secured in their own parititon)
That's what I do and it is rock stable.
Hope this helps!