I found a workaround for this problem, which allows me to use Intel Rapid Storage mirror with SSD 320 drive pair. Although the LPM disable via registry entries for DIPM and LPM and LPMSTATE did *not* work, going into the Power control panel and setting the power option to disable "Turn off hard disk after" did work!
Start Control Panel, Search for power, select "Change power-saving settings", for whichever power plan is selected (I use Balanced), click "Change plan settings". On this page select "Change advanced power settings". This brings up a small Power Options window. In the Power Options window, scroll down to Hard Disk, and click on the + to expand it. Click on the + "Turn off hard disk after", click on the Settings Minutes, and down arrow the value to Never.
Then click Apply. By choosing this setting, now my SSD 320 mirror does not hang, after 12 hours of running. Furthermore I removed the DIPM/LPM/LPMSTATE settings from the registry, and also find they have absolutely no effect. I have no hangs by setting Turn off hard disk after: Never, and without entering those registry settings.
Finally I will comment the common posting of the LPM registry settings shows entering a value for parameter LPMDSTATE (with a D), and according to this Intel documentation there is no such parameter. The parameter value is LPMSTATE (no D).
I hope this may be helpful to others seeing Windows 7 hanging with the use of Intel Rapid Storage and SSD 320 drives.