So I've used a tv as a second monitor before, that being my 26" Vizio, through an HDMI to HDMI to DVI adapter. Got it to work no problem.
I now have a 24" Orion TV that actually has a VGA port, but unfortunately I don't have a second VGA cable ATM. I would use an HDMI cable, but my tower doesn't have an HDMI port. That and my HDMI to DVI adapter broke SO I simply decided to use my new Orion TV as my main display.
I put it on the "PC" input and simply switched the VGA cable from my old monitor to the TV, but I get a "not supported" signal when I plug it in. When I take it out, it goes back to "no signal". Not understanding why this is happening considering all the manual stated I needed to do was plug the VGA cable in and switch over to the "PC" input.
Switch back to your monitor, drop the resolution to something low, then switch back to the TV. Re-adjust the resolution once you're on your TV.
I had tried a lower resolution and it didn't work, but I just took it down to the minimum resolution and did what you said and it works. Only problem is it's below 1280x768 so shit is slightly falling off the screen. I have it on 1280x720 and the screen starts at the first item I have on my task bar (running W7 BTW). Some items on the screen slightly shake as well. I considering taking it back and getting an actual monitor.
To continue what you've already discovered to fix it, as it was what I actually did, I would suggest just googling your television and finding out what the perfect specs are. I used to run mine through a 42" and, somehow, it seemed things were being cut off on the edges of the screen no matter what res I used. I googled it, and I can't remember exactly what I d/loaded, but I know that in searching for information I found exactly what I was looking for. I went from Not Supported, to poor picture, to things being cutoff, to perfect through the help section of their website.
Maybe something you tried straight away, but hopefully not and it sorts it. good luck, man!