Have you installed Matrix Storage Manager 8.9 ? as this is known to cause problems?
What I suggest you do is let it rebuild the array doing so will not change any data and may let you boot the OS on the array normally after it is done.
You should even now be able to see all your data as its rebuilding (if not My computer Disk management if not drive letter is not set right on the partition and open) to check that “iaStor.sys” is in \WINDOWS\system32\drivers .
Your post inspired me to continue to attemp to write the iaStor.sys file back to the location you mentioned. \WINDOWS\system32\drivers
I was finally able to accomplish this by attempting to install a 32 bit copy of Windows Vista Ultimate. The install CD was not able to help me locate the XP OS, or Repair the XP OS, but it did give me the privelage of having a dos C:\ prompt.
I selected the C:\prompt and found that I could copy the iaStor.sys file directly from a Driver Disc I made from my ASUS System CD. Good 'OL DOS and a Floppy Drive saved the day. Once I copied the iaStor.sys file back to the \WINDOWS\system\drivers folder, I was able to boot the system under last known good configuration. The RAID array is currently rebuilding, and I plan on pulling all the data I need off the array, and wiping the machine clean.
Thanks again for your help.