Ronin - hopefully it is during the day and the windows are facing the podium, providing it with good illumination. Is your 70-200 the IS? If you use that lens, regardless, you'll want to be at least at ISO 800 or 1600 so you can use a fast enough shutter speed to eliminate possible lens/camera shake. If it's the IS version and you are very careful - and not using flash - you can get away with 1/125th.
But as Evan says, you really need a shoe mounted flash if you intend to do these from now on. If the podium is back lighted by the windows, that is about the only way to properly illuminate the subject. I've done weddings in modern "glassy" churches and these are always a challenge, but can be done if:
1. You have a firm understanding of exposure,
2. Pay attention to the strongest light source,
3. Remain aware of where that main source is,
4. Be aware of what #3 is doing to your metering.
Regarding my 4th point, this is why it's often necessary to run your camera in Manual mode, after getting a good meter reading on the subject, and locking it in so the windows don't throw and underexpose your facial shots horribly. You can do this in two main ways: Either (a) get a spot meter reading off the podium/speaker using your zoom - a reflective reading, or (b) getting an incident reading from the speaker's position.
Likely my (b) suggestion won't be easily practical, so try to get a reliable spot reading. Have fun, and let us know if you have any more questions.
- Stu