Thanks to all who replied with suggestions as to how to remove masking tape
from a painted aluminum window frame.

After trying a few of your suggestions, we found that the easiest way to
remove the dried on masking tape was by applying heat with a hair dryer.
Then it peeled off quite nicely. It did leave a glue residue behind however
and we tried Donna's suggestion of using "Goo Gone" to get the glue residue
off. It was easy to get the glue residue off with "Goo Gone" - a great
product.

Also, as suggested, I will definitely use the green painter's Masking Tape
from now on as it is easier to remove.

Thanks to all who helped! Peter