Thanks everyone. I was able to return the replacement windows to Home Depot minus 15% restocking fee
and went to Lowes and bought new construction windows. This is really the best way to do it. Thanks
for the suggestions though. It seemed like it was going to be as difficult making a modification
tothe frame than it would to just stick new ones in.

Tony-

You bought new construction windows? Did you buy the whole window
unit, frame and all, OR just sashes? Be careful with terminology.
Sometimes it's confusing.

If you bought whole units (frame and all), you still need to consider
installing a moisture barrier between the new window frame and the
house's rough framing.

Sonny