Duplicate contents big no no with the search engines Dave so it could effect your rankings
Dave,
It won't affect you at all. Even if it was identical, it's on a different domain and more importantly, yours was indexed a long time ago.
Re; Rip off. I've had the same thing with a friend's site. An employee left to set up on their own. They have ALMOST stolen the copy word for word (which took days / hours to write).
They have even put my friend's company name in their keywords tag AND used photographs taken when he worked for my friend (of their jobs) on his new site!
There's some right poops around.