If you have more than one output on the graphics card (most likely the case) you can leave it connected and just have a second cable running to your receiver/projector. You can then use screen mirroring to display your desktop on the original monitor and on the projector.
If not you can also use a splitter to split the output to two locations. They are pretty cheap but not as good as a direct connection. If you use HDMI it can carry audio so you can hook an HDMI cable from your PC graphics output to the input on the receiver and then hook the receiver to your projector and speakers.
If you only have VGA out or something like that then you would have to run a VGA cable and audio cables. VGA can also be split if need be and there are VGA to HDMI adapter dongles out there but again a direct connection is better.
One thing to keep in mind is the length of your run. If your projector is 50 feet away a standard HDMI cable won't be sufficient and you will need a repeater or HDMI over Cat6 solution, etc. For shorter distances you might be fine with nothing but a cable or possibly a powered type like Redmere.
You would likely also need to be comfortable with a fish tape and run wires in the wall (plenum rated or better cabling) or comfortable paying someone to do it. (I assume your projector is in an different room than the computer and you don't want to jump rope over cables all the time)
Post more specifics about your hardware and what you are trying to set up and I can possibly give you more guidance if this info isn't enough to get you started
computer output 1 to computer monitor plus:
computer output 2 to receiver input - receiver output to projector input
computer output (VGA) to receiver input and computer output (audio) to receiver input - receiver output to projector input