50 and 60hz are basically the different scan-rates that are left over from the NTSC and PAL days. But even those are disappearing because in Europe, most video games now run at 60hz and all HD DVD and Blu-ray discs also run this way. The two different scan-rates (50/60) are basically the leftovers of the old PAL and NTSC systems.
When you put an "NTSC" DVD into your DVD player now, it's very likely you're not actually watching it in NTSC at all. You'll be watching a picture that has some of the same characteristics of the old NTSC system - that is, 480 lines, 60hz scan rate - but the colour won't be NTSC, it'll either be RGB, Analogue Component or Digital Component depending on what type of connection is being used to get it to the TV.
High Def consoles: I think for HD signals, they only use the 60hz scan rate (like NTSC does). So with HDTV, there are still different standards for Europe and America... but in Europe, a lot of the stuff just uses the US standard because all our HDTVs support it anyway.
I hope that makes some sense!
The reason im asking is i brought my dad a Linksys Media centre extedner (compostie or componetnt out) and the guy is selling it as its NTSC and wouldnt work on his set!
If you connect through Composite - you'll get NTSC, the real deal, in all its 1950s-style glory. If that works in colour, then your TV is NTSC compatible.
If you connect through Component, you'll get what's referred to 480i, or perhaps a choice of other (HD?) resolutions as well.