Nvidia 5900XT to 7800GS APG

Hi...
Sorry if this is a vid card newbie question...
I am in the process of upgrading my graphics card to a 7800GS AGP. Do I
have to remove the old video card drivers first... or just overwrite
with the new drivers?

Also my monitor is an older 17" Ilarma CRT with a 15 pin 'D' plug, I
notice that these new vid cards don't have a 15 pin 'D' socket... but
two square(ish) looking jobbies that I think are called DVI...? I have
a single adaptor from DVI to 15 pin... but which of the two DVI sockets
do I use? Will I loose half the graphics output by only using the one
DVI socket? Again, apologies if I am being blonde here... but I have
not messed with these newer cards before.

Dave