By way of example, I converted the previous snippet into this, which runs
on my machine in Script Editor. Hopefully it will work in yours too...
-- Brian Johnson
set this_url to "http://www.apple.com/index.html"
set local_filepath to (path to desktop) as string
set local_filepath to local_filepath & "a.b"
display dialog local_filepath
with timeout of 100 seconds
tell application "URL Access Scripting"
set x to download this_url to file (local_filepath)
replacing yes without progress and unpacking
end tell
end timeout