Normally everything is plug and pray (play). Once you turn off the computer to install the video card, the windows tell you new equipment installed, (duhhh) and then it will will ask you to install software or use the windows generic drivers, choose to use the drivers for the card you bought. I am not sure what your doing with the other video card, but you will have to turn off the onboard video card if you have one, or are you just replacing an old card? As far as the USB mouse goes, you should be able to plug that bad boy in, and it will start working, unless you are using a computer from the Apollo days.
Kevin