If xbox, dvds, and Standard definition TV are your needs get the 42in EDTV. 480 lines of resolution are enough for your needs and you sit far enough back not to notice the screen door effect.
If a HD programming subscription, HTPC, WMVHD, Xbox2 are your wants or are in your future (and you know what these stand for) then go for High Def TV's. Don't be like my parents and get a 52 in JVC HDTV LCOS rear projection, then complain about how lousy regular cable looks on it. I also advised them to go for the Panny 42 EDTV or another 480p plasma. NEC also makes a strong 480p plasma, so is the newest Zenith.
"Oh but it's digital cable, it should look better than this, right?"
No.