Thanks Mark for a great guide.
I just stumbled across this whilst trying to solve an issue I am having with additional <br> added to vmMainPage, trying to find which file this is called from, will be starting a new thread for support.
Have been playing with VM for over a month now and struggled on certain aspects, even using the developers manual.
There are refernces to content to/from the dev manual, not sure which came first, but this should certainly be added to it.
It may also be worth including that the debug option can be turned on within VirtueMart > Admin > Configuration > Global Tab > Core Settings > Debug
Ones this is turned on, handy little information icons appear next to each element within VM that show where it is generetad and at the bottom of the page is an additional table containing further information.