My PC has 3 7200 drives. I am currently using one for System (actually 2 partitions, since I am using a dual boot in my transition to 64 bit) one for project files and sounds; and one for backup. I’m wondering if I should move the sounds to another drive. I have 300 Gb of sounds and it occurred to me that when I record 8 tracks of drums at the same time playing back some large samples, I must be pushing that drive pretty hard. Seems to me that it’s needed a little more first aid recently too. So the basic question is: optimal set up - sounds and songs on 2 different drives? Thanks very much for your time.
I think OS, projects, and samples on individual drives is the preferred setup. You can always use an external drive for backups.
I would move the sound files to the other drive and buy an external HD for backups.
You could also put the project files backups on the soundfile drive, and buy an external HD for another backup, never hurts to have more than one backup ( I have a minimum of 4 ) on different drives.
I see Scab Pickens has posted a reply while I am so I agree with him too 
I agree - no such thing as too many backups.
I run an 80GB SSD for OS, two 1TB drives for projects and samples, and a third 1TB drive for general storage and backups. Then I backup system images to one external drive and projects to another.
I would configure as:
HDD1 OS partitions
HDD2: Project files
HDDS3: Largest drive
Partition 1: 350GB: Samples
Partition 2: Remainder: Backup
The partition just bigger than the amount of samples contrains head movement, ensuring minimal average and peak access times, allowing lower latencies. You could also make the project files on a partition of its drive for the same reason. SSDs do not require doing this, as they are truly random access without time penalties.
The backup partition would never be used at DAW critical times, and it is on a different drive to the critical project files.
Of course, ALWAYS save to an external or NAS drive. Then you will have two spare copies. The external/NAS could also contain a copy of the samples.