but you must select that card as the audio device in your sound properties
Yeah, good point. In fact, I would uninstall your old sound drivers first to avoid conflicts. In fact, if me after I uninstalled the old, I would reboot and immediately go into the BIOS Setup Menu and disable your on-board sound (if not using a card). This will prevent Windows from seeing the on-board as "New Hardware Detected" again and attempt to load those drivers instead. Then Save and Exit and boot normally.
If using a card, I would uninstall the drivers and shutdown, power off and unplug the computer from the wall, then pull the card. Then install the graphics card and go from there.