I wanna know which will be more cost effective?
2) dvd player vs cpu : will a dvd player give better performance like video n sound quality!
An HTPC can give you MUCH better performance and with a decent sound card, much better audio quality as well, as compared to a DVD player.
3) speakers : are de multimedia computer speakers good enough as the proper audio systems?
If you go in for a desktop PC speaker set - say a Logitech z5300 or a z5500, then yes, they are decent but if you're really serious about the home theater, you should be willing to spend more.