Switching video card brands

[Jon N <jdnandroid@gmail.com>]

I hope to be installing Debian in a new computer in about a week or
so.  It will have a Haswell processor and I hope to be able to get by
with the built in video.  But, if it doesn't work well I have an
Nvidia 8600GT card I can take from my old system.

But, I really don't know what's involved in switching.  If the Intel
video drivers are installed and I shutdown, install the Nvidia card
and reboot I assume the system won't load X, although I'll have the
command line to work with.  I have a little experience with Aptitude
and apt-get, will installing the correct drivers remove the old ones?
And what package name would I have to use to install Nvidia's drivers
from the repository.  I have (almost) always used Nvidia's drivers
downloaded from their site because when I search in Synaptic for
nvidia I'm not sure which packages I need to install.

Thanks,
Jon