No you can't , the rules are completely different.
You'll find the answer in the Warhammer Rulebook or in the army book you are playing.
Planetary Empires is Gamesworkshops answer to that. It is a customizable board and has rules for a Warhammer 40K campaign.
If you mean Warhammer Fantasy, Gamesworkshop sells it.
warhammer 40k or 40,000 is the year. It is 38,000 years in the future.
If you mean the MMORPG "Warhammer Online", the answer is yes.
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.
AnswerAt the moment, GW do not make a set of rules for matches like that, so no, 40k armies can not play FB armies.== ==
No, each types rules are very different. There are some models that are used for both games, for example some chaos demones, and demonetts.
You'll find the answer in the Codex:Chaos Space Marines.
Unless you are using Night Fight rules, they are useless.
Warhammer 40,000 was started by Rick Priestly in 1987 as the futuristic companion to Warhammer Fantasy. As of 2008, it has been around for 21 years, and is currently in it's 5th edition of core rules.