Hello,
1: In order to use dual display you eighter need a card with two VGA outputs (like the Matrox DualHead cards) or two graphics cards (eighter 2 PCI or 1 AGP + 1 PCI).
After installing both cards you can choose eighter to expand the desktop to the other screen or just to view the same screen twice. That's done in properties of display.
2: Go to
http://www.tvtool.de and choose your english language. On that site all things referring to TV out is explained very well.
3: No, the sound still gets out form the sound card. The TV-Out only sends video signals.
The easiest thing is to get a SCART adapter (it's cheap), then connect TV-cable (normally S-VHS) to SCART adapter and also connect sound card with SCART adapter via a Y-cable. Then you send both video and audio signals to your TV or video recorder.
Hope this helps.
RJ