The good news is that the knoppix iso is relatively small compared to your drive size so even with the 1-2 minutes (an eternity in computer terms) only about 1% of your drive is overwritten, and most of your data is not wiped. If it were wiped, then even trying recovery would be almost impossible without huge cost.
Before unmounting the HDD, the system still had the original disk partition information in memory, as well as the filestructure. Since you did not go through the normal filesystem driver code, it had not noticed the underlying disc blocks had changed, and everything looked ok (but wasn't).
If you had not yet, you could have written down the output of fdisk -l, because that is a good way to start trying to restore the partitioning information. Once that is there you might have a chance to restore the filesystem(s) and try to use any redundant information (depending on the filesystem) to restore things.
Since you indicate connecting the drive to a Windows 7 machine, you probably had a VFAT or NTFS on the drive, which AFAIK have less recovery information than some of the Linux native filesystems.
PhotoRec will try to find files by combining elements of files that fit together. Depending on the fragmentation of the file, that can be a lenghty process, so trying to recover the partitioning and then the filesystem should have priority.
The first thing to do (if you don't alreayd have done that) is buy a 2 TB drive and make a copy of the 1Tb drive on there, so you can restore the 1TB drive restore to its current state when necessary (a new drive might be an investment but it will give you a backup device, irrespective of whether you get your data back).
Then try to restore the partition information. If you still know how you partitioned it, you can just try to do the same commands, no formatting of new partitions at any time!. Don't do so before you have made a backup copy of the whole drive!
If there were multiple partitions on the drive, then there is a good chance that all but the first can be complete recovered, once the partition information is restored.
Then try to recover the filesystem (tools depend on the type), if it is VFAT or NTFS, it might be that you better look for Windows based tools for that.
In parallel you can try and run PhotoRec on the backup copy of the disc, as long as you don't change the actual backup copy, just pull any reconstructed files from there and copy them to a new location, outside of the backup.
It is difficult to give you very concrete steps to take as much depends on the actual partitioning and filesystem types, sorry for that. I hope this helps you on the way to get some of your data restored. (Did I mention to make a backup of your disc before trying any changes?)
