Answer
At the moment, GW do not make a set of rules for matches like that, so no, 40k armies can not play FB armies.
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Warhammer 40k & Lord of The Rings
AnswerWarhammer 40k started in 1987.
Defineitley 40K.
AnswerThe Warhammer universe is set on one planet but in the same time as Warhammer 40K. This is because it is a primitive planet left behind by modern humans (the Imperium) and they started becoming primitive - it is not the Earth.
Unless you are using Night Fight rules, they are useless.
If you mean Warhammer 40,000 and Warhammer Fantasy Battle witch Warhammer online is based there was in earlier versions of the games, But much of i has been changed in the current incarnation.
Answer Warhammer Epic is much smaller than 40K. It is also cheaper.
Answer 40K is a mini war game were two or more people collect miniatures and then assemble, paint and battle them.
Games Workshop made the Warhammer 40k Tabletop Game.
From what I have seen in stores in terms of selection and availability and forums with both subjects it looks that Warhammer 40k is more popular. Though their difference in popularity does not seem to be much.
This rule can be found in the Warhammer 40K rulebook, but due to copyrights we are not allowed to answer this question.
The Shred is the preferred enemy in the special rule warhammer 40k