First of all, DVI does not include any audio, so yes you would need a separate audio line to the TV or else you can buy an expensive DVI+SPDIF to HDMI adapter and then use an ordinary HDMI cable to carry the digital audio + digital video signals to the TV. Personally I use a separate analog stereo audio connection from my laptop to my TV and a DVI-HDMI cable, since my TV has 2 HDMI inputs with extra analog audio inputs. Usually the audio quality doesn't matter much with TV speakers anyway.
Second, I suggest that if you intend to use the TV for video or gaming, you might consider getting a 5:1 or 7:1 home theater audio system with a SPDIF input for connection to your PC. That's what I plan to upgrade to in the near future - IIRC Panasonic & Samsung offer Blu-Ray players with 5 or 7 speakers and a subwoofer, with optical and SPDIF inputs. Of course you could already have a BD drive on your PC, so maybe that would be overkill. The advantage of the HT audio system is that you don't have to boot up the PC to watch a hi-def movie.