For the benefit of lurkers, I also since discovered that DigiGuide (www.digiguide.com) channel logos which are stored on my PC as *.ch files are, in fact, actually std *.PNG files, and as such they import directly into the iProntoEdit Gallery.
Only problem with most of the logo sites and also the .ch files in Digiguide is the quality is a bit suspect. I spent an evening trawling the channel web sites and getting higher quality logos, then using the PSP buttonize feature created a set for myself. Some examples below.
Still got more to do but done most of my main channels thus far.