1. Displaying graphics on a TV monitor usually results in better image quality (compared to monitor), but you might have problems displaying text. It'll be perfect for playing SNES games though.
2. It's rather high. You should try to keep it below 50 celcius at least. Get a better CPU heatsink/fan or put in some case fans.
3. I would trust ATI cards for video-out. They're generally known to have better support for that kind of thing. Plus ATI cards have an overall better image quality compared to Nvidia cards.
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CPU: Intel Core 2 Quad Q9450 @ 2.66 Ghz (Yorkfield) Mobo: Intel DX48BT2 Memory: 2048 MB PC10600 DDR3 Videocard: PNY Geforce 9800 GX2 PCIe w/ 1024 MB GDDR3 Soundcard: On-board SigmaTel High Definition Audio Hard drive: 300 MB Maxtor & 1 TB Hitachi Optical drive: LG GGW-H20L (2x BD-R DL) OS: Microsoft Windows Vista (32-bit)