This didn't work for me either. I had to get a DP to DVI cable then a DVI to HDMI cable; then everything worked fine.
I picked up a DVI to HDMI cable at the Apple store to connect my 2008 MacBook Pro laptop running 10.6.1 to a Samsung SyncMaster T240HD. I plugged the DVI into the laptop and the HDMI into the monitor; the laptop recognized the monitor and allowed me to set the res to 1080p for it, but the monitor gave me a 'no input' signal. I tried mirroring on and off, but nothing. I tried each input setting on the monitor as well. Any ideas?