TH-50PHD5B or TH-50PHD5BX (or TH-50PHW5B or TH-50PHW5BX) means British edition, also to be seen are TH-50PHD5E (European) or TH-50PHD5U (USA) and other letters too; this part of the code signifies country. If it doesn't say B or BX at the end it probably means that it's imported from European mainland, and will have different warrenty conditions.
Additionall, TH-50PHD5 or TH-50PHW5 with letter D or W means colour of bezel, where D is black and W is silver and A means silver with speakers.
Finally, TH-42PHD6 vs TH-42PW6 is resolution where H means High Definition and absence of H means Standard Definition.
Therefore code is:
TH-[screensize]P[resolution][bezel-colour][generation][country]
I think the P is for PAL, T is for television, H is for plasma (x for CRT or LCD).
The only difference between a "W" and "D" is the colour, although you may have to buy a component input or other card for the black model (it may only have a VGA connection). So, you may have to buy an input card, but they are less than £500. Aks you dealer what connection you will get with screen.
StooMonster