Crossfire, how does it work?

I'm thinking about getting an ATI Radeon X1900XTX, now some friends told me, if I want to crossfire that, I have to get cards that are crossfire ready/edition, my question is, do they have a Radeon X1900XTX crossfire version, or can I use a regular one of that, and a X1900 Crossfire Edition, how would I work this.

My main quesion is, what cards are needed to do this, they have to be on the same level, so can I just get 2 X1900XTX, or do they have to be special crossfire editions.

And do both cards have to be like that?

 

The primary X1900XTX is just a plain Video card, but the second card is your crossfire card (the special one).

This is what the crossfire edition looks like:
http://i59.photobucket.com/albums/g305/ianthegeek/ATI_X1900_Crossfire.jpg

So, the answer to your question: You cannot by two of the same card and connect them, you need one X1900XTX and one X1900-Crossfire Edition.

Sidenote: There may have been some confusion because Nvidia series cards is what you would use if you wanted to buy two of the same cards, and you would connect those in SLI rather than crossfire