That is a GREAT question Muneernk.

I see that my device id's are already set in the vanilla AppleIntelPIIXATA.
I have tested so many different AppleIntelPIIXATA all panic.

I have tried my 10.5.8 file - panic
I copied my plist ICH data from 10.5.8 to 10.6 - panic
If i remove AppleIntelPIIXATA - waiting for root device.
Netkas' Intel ATA support for Snow Leopard - panic

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iDeneb v1.4 10.5.8 Vanilla
MB: Intel DG31PR (ICHx,USB,PS2 Fixed)
CPU: Intel Core 2 Duo E4500 2.20GHz
Video: PNY-NVIDIA GeForce 9800 GTX+ 512MB (Install with onboard Video, Add EFI String to boot)
Ram: Corsair 2048MB PC6400 DDR2
Audio: Realtek ALC888(ALC88X Fixed)
Net: Working out of box
HDD: 3 SATA / 1 IDE (Win Xp, Win 7, OSX86)
CD/DVD: LG -R, -R DL, -RAM, -RW, +R, +R DL, +RW

Snow Leopard install in progress.