Piggy back video cards?

I have a dual core and I have a nvidia 8600 gt -256mb video card and I want to piggy back the same in my other slot but my question is can it be a different maker? I know I have to use another nvidia 8600gt but what about manufactuer?

Also is there anything special I need to do when installing it or will my comp just automatically pick it up and see it after installation?

they recommend you use the same manufacture, but in reality the chips and board design is dictated by nvidia so they should be identical hardware wise

im not so shure about the cards bios tho

ive only used SLI along time ago. with some 3dfx cards, back then it was 2 totally different manufactures, and once they were in windows really didnt do anything much and all was good