Cailin, I don't bother with parboiling. I just cut them in half (or quarters if they're medium/biggish or eigths if they're whoppers) and chuck them in with a good splash of olive oil and whatever seasoning I'm in the mood for.
My brother puts a splash of boiling water in bottom of his pan with the olive oil and seasoning - but it didn't work well for me when I did it.
I usually put them on about 45 minutes before I expect the roast to be ready. So it's 45 minutes plus the time it takes to make gravy and get plates out.
For potatoes I think the variety can make a big differance. I like the Coliban because it's usually at the supermarket but if you have a better greengrocer they might help you out by suggesting a better potato.