Err, no.
You have a TV card. It has (at the very least) coax-input. It SHOULD have RCA input as well. Plug your Dreamcast into either of these plugs and it'll work fine. At a lower resolution. (You knew there was a catch, didn't you? 😉 )
If you want the "full" 640x480 resolution that the Dreamcast is capable of and a "better" picture, then buy the card. This is the optimal situation. You can play your games on your monitor as well as the TV. Pretty darned cool. But if you're a cheapskate like myself, then you'll do the first option as it doesn't involve spending any more money.
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And I was beat to the punch. 🙂 Plus, a better explanation!
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