I'm having trouble with this graphics card, need help asap.?

I recently bought this graphics card, the radeon 9800, and I'm having trouble getting it to work. Its the righjt kind of graphics card (My pc has an agp slot and this is agp) and I have the driver and I can connect power to it, but its till not working. I'm not on that graphics card right now, because for some reason it barely works. This is my process for installing it, please tell me if I'm doing something wrong 1. With my normal graphics card installed I download the driver or load it from the disk (I've tried installing it many times) 2. Power off pc and install the graphics card 3. Start my pc up and hope for the best. When I do this, different things have happened 1. My pc seems to go down to a generic graphics output as it is very slow 2. Everything loks messed up, there are red and blue lines and splotches on the screen and the mouse won't move. Please if anyone can help I'll try anything to get this to work.