Here's what I know: All Macs that have bootcamp available to them DO in fact have BIOS. BIOS can be implemented in traditional way and on top of UEFI. For example I have a laptop whose UEFI only does almost nothing else other than starting BIOS.
Now for the graphics card part: I'd recommend that you wait for officially blessed card for macs.
Now for BIOS part: If windows 7 is configured to use UEFI, then you will have problems with video card. On the other hand, Apple is using obsolete version of UEFI, so it is quite possible that windows is only using BIOS emulation.
It is also important to note how UEFI and BIOS are used. Basically, systems main board has the biggest part of firmware. Once the system is started, it will load firmware form other devices such as video cards, network cards and so on.
Today almost all accessible video cards have firmware which will integrate with BIOS. Some cards also have firmware which will work with modern versions of UEFI. Now the question is how many cards will work with obsolete UEFI specification used by Apple? As far as I know, only officially blessed cards will, but I could be wrong.
Now I'll get back to windows: If your windows installation is using BIOS (and I believe it is), then your non-blessed video card should work fine with it.
Also, I had contact with hear-say that non-blessed video cards will work fine on windows, but I still believe that it would be best to test it out and be sure.
The safest way would be to obtain some relatively recent PCI-E video card and try it out. Surely you must know someone who could borrow you one. If not, then it may be economically justified to buy cheapest one available and see if it works on windows.
Also, just to clarify, UEFI was called EFI back in the version Apple is using.
