The Washinton Metro bus 5A runs from DC to Rosslyn to Herndon to Dulles. I've taken if from Rosslyn to Dulles. It costs $1.10 and runs once an hour and lets you off at door #4 on the center level.

If you have an eticket boarding pass you can go right through security to the gate and check in. You can also do curb side check in if you have baggage.

The biggest delays I've seen in the 5 flights I've taken since 9/11 have been people waiting at the ticket counter.

So if you catch the bus at Rosslyn or the Herndon park and ride just off the tollway you can cut your time down considerably. If you use an eticket that cuts it down even more.

Last Monday I left Rosslyn at 1:45, got to Dulles at 2:30, got through security and rode the shuttle over to terminal B in less than 15 minutes, and was in plenty of time to catch an earlier flight than the flight I was scheduled to take.

So 3 or 4 hours is way too much lead time.