I have an HDMI cable hooked up to a graphics card, but not the sound, which is integrated into my motherboard. Is there some sort of adapter I could use so I can hook up my cable to my graphics card through HDMI and plug in audio with a 3.5mm jack? Please help
THe sound that is passed over HDMI is digital and is "mixed" in with the video signal. I doubt there is an adapter to do this and if there is one it is likely very expensive. Does your video card support audio via HDMI? It most likely does and if it does you can assign your audio out to the HDMI port. The Radeon 5750 5770's do this in windows 7 with no special provisions.
What is your video card? OS?
Also the device you are connecting to has to support the hdmi audio and cannot be a "pass through" device.