Absolutely, if the video you are watching has a AC3/DD or DTS track and you set up Media Center or whatever video player you are using to pass the AC3 bitstream through.
Normal system sounds, games and music will only play in stereo, unless your motherboard features DD Live or DTS Connect, which encodes sound on the fly into DD - but can be a hassle as it doesn't alwasy work well with pre-encoded movies when it is switched on. Meaning you can end up having to change the settings back and forth very often.
If you're sending HDMI straight to the TV, I'm guessing your receiver must not support HDMI? Otherwise multichannel LPCM over HDMI to the receiver is the way to go.