My tv has a D connector PC connector. Is it just as simple as connecting a cable from my Video card (GTS250) to the TV? How do I get the sound to the TV speakers? Would it be better to connect to an open hdmi port instead of the D connector? Will the sound come through via the GTS250's DVI -> DVI/hdmi adapter -> hdmi cable -> tv? Will my PC be able to act as a Bluray player then?
Plain and simple, if you're wanting to play Blu-Ray movies from your PC to your HDTV, just connect the two via an HDMI cable (you will need the appropriate software to play blu-ray movies as Windows 7 doesn't do it natively).
You can connect your PC to your HDTV via the D-Sub 15pin connector, but this will not carry audio. A separate cable will be needed to carry audio from the PC to the HDTV. Normally, there is a PC Audio connection port near the D-Sub 15pin connector input on the HDTV. Note that you cannot play DRM protected blu-ray using this connection.
The DVI --> HDMI connection can be a bit tricky. Not sure if the GTS250 you have has the ability to accept audio from the motherboard/sound card. If it does, there should be a 2-pin audio input somewhere on the graphics card. This would connect to your motherboard's or sound card's audio output. If you google audio over DVI, you should be able to find more information. Note: I have no idea if blu-ray videos will play over this type of set up.
Your best bet... HDMI out from your graphics card to HDMI input on your HDTV.