My house was built in 1989. Most of the builder grade, double pane,
double hung, aluminum frame windows have ruptured seals and are fogged
up. I am considering repacing them myself but have no idea how to
remove them.

The original windows seem to have a flange that has been nailed to the
sheathing before the siding was put on. The house has aluminum siding
and also brick veneer, and I don't want to damage either when tearing
out the old windows.

The interior is drywall boxed in around the window openings with a sill
made of a corian looking material. Damaging the drywall would be easy
enough to fix, but I'd like to avoid that too.

I take on a lot of home repair projects and get good results, and I
assume I have all the tools I need. I just need some direction here as
to how to start.

One final question, and I suppose this is something all DIY people need
to ask themselves at one time or another: Will there be any real
savings buying windows from Home Depot and installing them myself vs
ordering from one of the many local companies, who I assume get them
bulk for better prices, and letting their crew install them?

Thanks,
Christopher