A skype camera for tv is has the rev elegant software loaded into the tv by the manufacturer itself. So only selected models of Skype cameras will work with it,either those manufactured by the same brand or some of them approved by the manufacturer. For e.g Logitech makes such cameras for Panasonic tvs.
While the digital PC camera has to have its drivers/software loaded onto the PC. The TV may not be able to recognise the PC camera due to software/hardware conflict in most cases.
There is a new type of Skype camera for tvs; which are stand alone - these work via HDMI inputs. This kind of camera has the software loaded onto its own hardware, so you can use it with older tvs as well provided it has an HDMI input. One is from Logitech again - TV cam HD and another is from Tely HD.
Regarding the wifi dongle, you will have to buy the dongle from the tv manufacturer only as the normal PC wifi dongles will not work most probably. Contact the manufacturer to see if they support dongles from other brands; Belkin was one dongle which was compatible across different brands but you still have to check with the manufacturer again before you buy one.
