The Panasonic TH-42PX50U is an HDTV plasma. The TH-42PD50U (notice the only difference in the model number is a "D" instead of an "X.") is an EDTV plasma. Both of these plasmas have tuners in them.
Apparently, Panasonic is now selling the TH-42PM50U thru Costco (notice it has the letter "M" which stands for monitor). This plasma is an EDTV plasma monitor without the tuner.
Some manufacturers sell special models with slight changes and different model numbers thru discount dealers such as Costco so they don't upset their regular dealers. Panasonic did this several years ago with their DVD players. They had a model 32 (other letters also) that sold thru the audio/video dealers, a model 27 which sold thru Target and a model 22 which sold thru Costco. These were all the same basic unit with only slight differences.
The plasma at Costco does not have a tuner. You can use anything that has a tuner in it or supplies a TV signal, such as a VCR, DVD recorder, cable box, satellite receiver (tuner) or set top box tuner (such as those from LG, Sony and Samsung) to supply the TV signal to the plasma. For people like me who have cable without a cable box, the simplist way is to attach the cable outlet video cable to the VCR and then into the plasma unit. DVD signals go directly into the plamsa.
This model is similar to Panasonic's commercial/industrial line of plasma's that come without a tuner or speakers such as the Panasonic TH-42PWD8UK which is an EDTV plasma. This Costco model appears to be the TH-42PD50U without the tuner, with speakers and a different appearance.
I saw this model tonight at costco but did not have time to check out the specs. It is very nice in appearance and has the speakers below the screen.
EDTV and HDTV are suprisingly close in quality. EDTV plasmas actually look slightly better than HDTV plasmas (from the same manufacturer) when playing progressive scan DVD's. The reason for this is that the progressive scan DVD is at 480p resolution. The native resolution of the EDTV plasma is also exactly 480p (there is no scaling involved). The HDTV's plasma's "scaler" circuitry has to up-convert the 480p signal to either 720p or 1080i (depending on the native resolution of the HDTV plasma). This up-converting process always causes at least a very slight degradation of the signal. For this same reason the EDTV plasma will also display a regular standard TV signal slightly superior to the HDTV plasma.
When fed actual high definition TV signals, only then will the HDTV plasma display a slightly better picture than the EDTV. However, this difference is suprisingly small. Also, it is only evident when viewing at 8-10 feet or closer on equal quality units from the same manufacturer. This is a well kept secret that most casual purchasers and many dealer personnel are not aware of. If you compare plasmas at a dealer make sure you grab the remotes and readjust all the settings to the same values. Don't judge the pictures you see unless you do this.
More important than EDTV versus HDTV is the quality of the glass and circuitry in these units. I would take an EDTV plasma from quality manufacturers such as Panasonic, Hitachi, NEC, Pioneer, JVC, Sony, etc. any day, than an HDTV plasma from brands such as Akai, Norcent, Maxent, Vizio, Sampo and even Samsung and LG. Panasonic is one of the few manufacturers that actually make their own glass and no one makes better. Toshiba plasmas, for example, have Panasonic glass. HP plasmas are actually rebranded Panasonics. If you don't know these secrets stay with the major Japanese name brands.
Presently, an EDTV plasma from a quality brand is definitely a best buy. You don't need High Defitiniton sources which cost extra from your cable or satelite company.
The EDTV will accept any digital signal including high definition signals. It will downconvert any HD signal to its native resolution of 480p. If you supply an actual HD signal to an EDTV plasma you will be stunned at the great picture you will see. Standard TV signals that are sent over cable for example but originate from HD television cameras for network news or the Monday Night Football Game look excellent in 480p.
I own a 42" JVC EDTV plasma and a 37" Panasonic commercial model EDTV. I don't need cable boxes for HDTV, have to pay for HDTV packages and I still get very good to excellent TV signals and superb DVD signals (using HDMI inputs). Finding Nemo is absolutely stunning on both units.
One last thing: plasma is still superior to LCD for several reasons including black levels, color acurracy and off angle viewing. That is a dicussion for another day. The burn-in talk is no longer valid with plasmas (the good brands have burn-in prevention circuitry). Just don't display static images on plasmas.
Hope this all helps.