A DVI switcher is one option, but there's another option. I have the same issue with my HDTV monitor which only has one DVI input. However, it also has two HD compatable component video inputs as well. I run my HD tuner to the DVI input and my older non-upcoverting DVD player into one of the component video inputs. This works fine for my system.
However, if you have a newer upsampling DVD player, you could connect it to the DVI input to take advantage of the upsampling feature, and connect your HD tuner to one of the component video inputs (assuming they are HD compatable). Look at the description on your TV, it should indicate 480i/480p/720p/1080i if the component video can handle HD.
My experience is that HD looks virtually identical through component video compared to the DVI input, at least on my Sony CRT HDTV monitor. However, the DVI may look cleaner if your set is LCD, DLP or plasma technology.
It won't cost you anything to try it before investing in a DVI switcher. Good Luck! JZ