Yes, depending on the connections your HDTV set has. You'll probably have to buy some additional hardware to get the signal from the VGA output to the TV's HDTV inputs.
Check out what connectors are on the back of your set.
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I've got both my computers hooked into rear projection televisions, one 50 inch Toshiba (just via svideo) and a 53 inch Sony HDTV.
You have to be careful of burn-in though. You don't want your expensive HDTV set to have your Windows taskbar permanently burned into the tubes. Keep your contrast and brightness way down low. (calibrating your set with the Video Essentials DVD is a good idea.)