You said until you get a new card with DVI outputs.. the new card may fix it (okay that's not really an answer). I really would expect most current hardware to support the kind of resolutions a 32inch tv can support, but it sure sounds like your video card is just limited in some way. Or maybe you need new drivers? That's an overused suggestion that in my experience usually doesn't solve anything, but it's worth a shot if you're stuck.
The thing is, you say how can you make that your default. When you change it it should stay that way. The fact that you have to keep doing it over makes me wonder. I have to think there's something wrong, but I don't have any easy answer as to what's going on.
Oh, and about the 16 bit thing.. eh.. perhaps your current video card has too little memory to support 24 bit color at the full resolution of the tv? I use a card which is capable of far higher resolutions than my 1680x1050 screen can manage, or more to the point higher resolutions than I've ever seen in any screen anywhere, but older cards would likely have lower limits.
Still such limits shouldn't mean you have to keep changing it to 16 bit on windows startup. Once you change it it should stay that way.
