You will have no problem installing a new graphics card before the drivers, this is easy.
The important thing is find out what your current and also your new graphics card speed is. 2X or 4X or 8X. The reason being that they require different voltages. If say you put an 8X speed card into a board that has been running at 2X then the chances are you are going to blow that graphics card. The solution is easy in as much you have just got to alter the graphics card speed in the bios.
To physically change the card without the drivers is simplicity. With windows fully loaded, delete the current card in device manager and shut the computer down. Take the old card our and insert the new one. Now boot the computer, it will come up in standard graphics 600X480. Load the drivers and you are away with the new card.