I am building my first desktop and before I order the parts I need to know if an integrated graphics core is needed in a CPU if I am going to use a high end graphics card attached through an expansion slot. If not is one required in the motherboard or can the graphics card just be plugged in?
If you plan to only use a dedicated graphics card, then no - the internal graphics core of the CPU would be useless.
Maybe you would be able to use something like Nvidia Optimus to save power by only using the dedicated GPU for graphically intensive tasks like gaming or GPU computing, and automatically switching to the internal GPU for everything else. However, I don't know if that technology is available for desktop computers.
In any case, the internal core (even in combination with the dedicated GPU, if possible) could only be used if your motherboard provides the necessary connections from the CPU to the southbridge, and some kind of graphics ports (VGA, DVI, DisplayPort or HDMI).