There are many *.CHK File recovery suites availabe. Based on this thread, I would like your opinion on which one to use.

CONFIGURATION
HDD1 - WD 80GB (Master)
* Removable internal hard drive on rack/tray
* Windows XP NTFS

HDD2 - WD 160GB (Slave)
* Fixed and bolted internal hard drive
* FAT32 data drive

SYNOPSIS
(1) Recently, I swapped out the WD80GB HDD1 with a Maxtor40GB HDD1. The Maxtor drive had Ubuntu Linux installed and I wanted to format this drive.

(2) I placed a Windows98 boot disk (FDD) in the floppy drive.

(3) I typed the "VOL" command at the prompt to ensure I was about to format the right drive.

(4) Once the right volume was identified, I formatted it. This type of formatting takes a while, so I left the computer and came back.

(5) When I returned, I swapped out the Maxtor40GB HDD1 (target of format) and replaced the WD80GB HDD1 (XP).

(6) When I booted into WIndows XP and attempted to view my data drive (HDD2). I saw nothing. However, it did show that 38GB were being used out of 160GB (my now invisible data).

(7) I turned on the view hidden files option, and still nothing.

(8) So, I shut down, and placed a another drive in HDD1 that had Linux installed.

(9) I booted into SuSE 9.2 Linux and attempted to view my data drive (HDD2). I saw two folders: found.000 and Recycled.

(10) I clicked in each folder, and much to my horror, found.000 had all of my files with a *.CHK extension.

QUESTIONS
Why was HDD2 affected by the format, when I only asked that HDD1 be formatted?
Why can't I see my *.CHK files in Windows, but the drive shows them as being used?
How can I recover these files in Windows mode, if I can't see them?
Is there a recovery method that will restore my data drive and directory structure to its previous state?

The problem happens because BIOS and Windows and some other OS don't all share the same view of the installed drives. It could very well be if you swapped your drives that Windows was using the address of your prior hdd2 and even though you thought you were clearing your new Maxtor it cleared hdd2. That seems to be what has happened.

I don't know what a Windows format does but if it wrote over your data, it's gone. If it just renamed everything to *.chk you should be able to do a painful manual recovery.

It's really best to use Linux tools for all your partitioning and formatting jobs as everything in Linux is visible and no surprises will pop up for you.