I assume that unRAID uses ext3 filesystem. Is there a tool, maybe anything even commercial to convert NTFS formatted drives to ext3 (or the Filesystem unRAID uses, ext2, whatsoever) so that they may be just inserted into an unRAID box and re-used without having to copy them? I know Acronis as an example would convert between filesystem, not sure if it will do NTFS->ext3 though and how reliable this would be? Any hints?

unRAID uses the Reiser FS and no there are no tools that I know of that will "convert" the disk.  unRAID does a special clearing and formatting on the drive so there is no way around that.  You will have to format the drive in unRAID or with the preclear script (look in the Custimization forum section) to get unRAID to recognize it.

Ok, I see, thanks for the quick answer to that! Highly appreciated!