In your case, you get both. I have an application that needs a
fullscreen window with no clutter. I simply open a new window with no
toolbars, scrollbars, etc. and size it to the user's desktop. The
user knows it's coming, and it doesn't affect the settings of their
browser.
But seriously, tread lightly on other people's settings. If you need
more convincing on this issue, consider the sites on the internet that
do the things you are looking to do. There are indeed site you can go
to that will resize your browser, strip off your explorer bar, add
bookmarks to your favorites, set themselves as your homepage, and
refuse to let you close them. Think what you do when you see this
happening: Frantically click the close button until they die, and
hopefully before they get too far with their scripting attack on your
browser.
Do you really want your site to be classified in this category?
Jason Kester
Expat Software Consulting Services
http://www.expatsoftware.com/