"OK. So you suggest I forget about using the drivers from the Isilogic web site for this SISAS controller and use these other drivers, correct?"
Yes. Keep in mind that while the PERC's are just rebranded LSI controllers, the original specs have been tweaked to Dell's specifications, so you are always better off using a Dell driver when possible. LSI should be your goto in the event that a suitable Dell driver cannot be found or doesn't work.
On most decent hardware RAID controllers, the OS is never exposed to the actual disks connected to the controller. The controller takes the disks, configures them in a "virtual" disk, then presents that virtual disk to the OS to use. For example, if you have two 500GB disks and configure them in a RAID 1 (mirror), the controller manages the mirror and presents the OS with what appears to the OS as a single 500GB disk. If you have three 500GB disks in a RAID 5, then the OS only sees a single 1TB disk, while the RAID controller manages writing/reading to the three individual physical disks behind the scenes.
So, yes, if you configure the two disks in a RAID 1, that will be presented to Windows as a single disk to use. It may not all be the C: drive - it can still be partitioned like you would any other physical drive. If you want to use the disks individually - say have two 500GB disks like you would on a desktop, you would configure each physical disk as a RAID 0 - the OS would then see two physical disks.
The PERC will support up to 64 virtual disks/RAID arrays, so you can have as many arrays on the controller as you can stack into a server.