New Hard Drive Set up Question

[rappy]

Forgive me if this is a silly question, but........my current set up is a simple WD 250GB hard drive along with an external WD 250GB drive. I just picked up a 150GB Raptor as well. I don't want to set up RAID, but I do want to make sure I set it up to optimize my system, and make sure I don't loose important info. I know I should make the Raptor my system drive, and I want my internal 250 drive (data) to store important files (pics/music/important docs....ect), as well as all the non-essential apps/files and back that up with the external hard drive. I don't want to back up "stuff" I can easily re-install if I ever have a problem on the external drive - just files I might loose forever - and yes, I WILL make CD/DVD back ups as well. But what exactly do I install on the raptor? Of course the OS, but my uncertainty is do I also install on the Raptor for example what I would cinsider:

essential computer files - examples are my video/audio drivers, Antivirus apps?
Hardware apps - Do I install my Creative Audio Console (and similar apps) on the raptor, how about MS office? I know I should save the actual files on my "data" drive but the actual app on the Raptor?

I hope these examples explain what I am trying to get at, and I wont go over EVERY add-on app I have installed on my pc.

Basically, I dont want to "bog" down my OS drive, with non-essential apps, but I want to make sure I do have the proper apps installed so that I can enjoy its benefits.

Thanks in advance,

Rappo