if you have a decent sized screen, surround processor, amps, dvd player, speakers + sub... AND a nice comfortable thing to sit on... I guess you wouldn't use a computer to watch a DVD...
nowadays, multi channel receivers are getting better w/more features... decent DVD players are getting cheaper... and there're many 5.1 speaker systems that deliver good quality at bargain price... about the only thing that's still hard to find is a big TV that you can live with for a while at reasonable price... if you dont' mind having a big heavy TV, you can get a home entertainment system you can live with for more than a few years... for just a couple grand... the only problem is that audio is like computer... if you get into it, you always get the itch to upgrade.. and before you know it... I guess we all know this shit...
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I do believe you can enjoy DVD on computer monitor... after all, I still enjoy music from my friend's 'boombox', crappy car stereo, or football on 14" tv on somebody's yard (and I bet I'll be doing that if I only had a yard)
about the only question I have is... do you move the monitor to your living room when you watch DVD? do you cram chairs into your room/office where-ever your computer is? or you all got huge rooms?