IIRC you have to save over half of each tribe.
One of the Christmas Lemmings' is a four level demo (not sure which year, I didn't know there were two of them), PM your email address to me and I'll send it to you. Holiday Lemmings (both years) is commercial and not available, so you'll have to hunt eBay or the Amiga game sellers' sites for that. Note that the '94 edition contains the '93 levels as well, so you don't need both.
Chris
