Files renamed to Unix how to fix this

I have upgraded from an old G5 to a new imac running on 10.56
I am using a Lacie ethernet hard drive on a network between the two new imacs to store and back up files which was recommended for this type of nature. Many of the files stored on the Lacie hard drive have been converted to Unix files, as I am aware this is due to the system not recognising the files when copied from the old hard drive to the new Lacie hard drive and the new imacs. I am also aware that I can rename the files by adding .tif, .pdf, .jpeg, .eps etc and the files should then view and open as their originally state, which is fine except in many cases I have hundreds of files renamed to Unix and would take forever to change them all, they also seem to lose their preview, if I add the .tif etc to them and then also need to be opened and resaved to gain the correct preview and icon, which makes the situation even worse.
How can I stop this happening and is there a way or some good software that can rename all the unix files back to their original format.
Please can anyone help or advise me with this issue as I have hundreds of files that I need to use and cannot use them as unix files and cannot possibly rename them all either. I also want to make sure that this does not keep happening with my future work too! PLEASE HELP!!