Are my layovers long enough?

This round trip will be my first time flying since I was much younger. My first one is 40 minutes in Denver and I have to get from one end to the other of the very long terminal B, United to Express jet. I understand that 40 minutes is w/o taxiing. So is this long enough to make my way to the new gate, assuming the flight is on time?

On my return flight I have to get from Terminal C to B at Houston Intercontinental Airport, it's Continental to Express Jet. From their map I've gathered they have some sort of In Security transportation between terminals but this time I only have 35 minutes. Again, will this be enough time?

I called Orbitz to see if this was long enough and when they called Continental they assured us that the flights were connecting flights which I assume means I'm guaranteed to make it or else they'll have to find me the next available flight. Still I was just wondering what those with personal experience say, because even the Orbitz guy said that was cutting it short.