Which 8800 to buy

Hello Guys. I'm upgrading my Mac Pro video card from ATIx1900 to the new nVidia 8800. I was reading a lot of things about the issues with the new card working only on new versions of Mac Pro. I now know that they have the card for both "versions" of Mac Pro. The thing is: how do I know what version I have?

I bought mine in June 2007. I know the "new version" is called "early 2008", and having bought mine in 2007 would probably mean it is the older version. How can I be sure? Can it be like cars were you buy a so called 2008 model in 2007?

If confirmed my Mac is the older version, that means the PCIe is 1.x right? Ok. The video card for the 2007 version is PCIe1.x or 2.0 with backward compatibility? 2.0 cards are supposed to work with 1.x and vice versa, so this new card is a "fix" that also works in 1.x or was it remanufactured to be 1.x?

Also, if my mac is PCIe 1.x, that means that even if I use a 2.0 card it will not perform as good as if it had a 2.0 slot right?

One last thing: I have vista on my Mac as well for games. Can I buy a PC card and put it to work on Mac intel? Even if it does not work on Mac OSX?

Thanks in advance.

I'm not fully understanding your post. If the 8800 requires a pci-e 2.0 x16 slot anything before will not fit it has to be 2.0 and x16.