Switching will allow you to input a number of the same type of inputs an and output the same like 3 components into the receiver and 1 output to the tv, and it will switch between them as you select the various different buttons. (i.e. dvd player, sat tv, cable tv)
Upconversion is when you input basically any type of input and you can output to hdmi.... i.e. input - svcd, component or vcd and upconvert it to and output via hdmi.
I have a upconverting Pioneer and Its great until I buy a dedicated Pre-Amp.
Its worth the extra flexibility for me to just have 1 HDMI cable to my Plasma tv that is in a different room from my equipment...
