Ok..
My old clones and editor are here:
http://ericenzwaan.nl/eric/lemmings/lemmix.htm

One of the reasons I want to make a new program is that there are made lots of custom levels with my editor (look for 'lemmix' on http://www.lemmingsforums.com/)
It would be nice to store them all into 1 database (maybe eventually online) and play them 'out of the box' instead of copying around.
Another reason is that the editor and clones are seperate programs (no shared code).