Windows Server Disk Performance Monitoring (Through APM custom WMI) - HELP

I need some help with disk performance monitoring.  We are in the middle of transitioning to a new SAN and need to keep an eye on server disk performance data (primarily Windows 2003 and 2008).

Select AvgDiskWriteQueueLength From Win32_PerfRawData_PerfDisk_PhysicalDisk

Select CurrentDiskQueueLength From Win32_PerfRawData_PerfDisk_PhysicalDisk

Select DiskTransfersPerSec From Win32_PerfRawData_PerfDisk_PhysicalDisk

Select DiskReadsPerSec From Win32_PerfRawData_PerfDisk_PhysicalDisk

Select DiskWritesPerSec From Win32_PerfRawData_PerfDisk_PhysicalDisk

3. I have created custom WMI performance monitors.  When I assign these to various servers, the data returned is an extremely large number (i.e. Disk Reads PerSec 50727533.00).  I'm more than a little dubious regarding the validity of the formatting.  On the Current Disk Queue Length I selected the check box to "Count As Difference".  I believe this counter is now reporting meaningful data.  However, I'm pretty much guessing on several of these options.

Any help on this subject would be greatly appreciated.

Thanks, Iain