So I am looking at flights to Argentina for the first week in October. I'm finding that most send me out of Lambert to IAD and then from IAD to Buenos Aires. However, there is all of one hour from landing in DC to takeoff to BA. Is that enough time to get from domestic to international terminals in that airport?

In my experience, no. IAD is the single most difficult airport to get around in because you are entirely at the mercy of airport buses. It is also currently under a major reconstruction (to eliminate being at the mercy of airport buses), which doesn't help. When I was flying in and out of IAD every 4 weeks, there were times I was stuck waiting for those buses for upwards of 30 minutes and so I couldn't leave the airport because I couldn't get to the exits in the concourse. Were it not for the only means of passage being the buses, I would have been out of the airport in ten minutes. Here's a terminal map. If you land in A or B and need to leave from C or D, you could be in a jam.

That said, I haven't (thank god) flown in to IAD in about a year now, but it's my understanding that the construction is still underway.

Damn, I should know this...I can see the IAD tower from my cubicle, but alas, I don't know. If your flight arrives at Dulles sometime between 9 and 5 however, I could potentially give you a ride from one terminal to another.