I'm pretty sure that it is not possible for an application to take screenshots on an un-rooted Android device. I believe that Google did not allow this for security reasons. If you want a convenient way of getting a screen shot onto your PC then use DDMS - http://www.b4x.com/forum/chit-chat/7145-android-screenshot-application.html
On the Archos 70, you can click on Settings, Applications, Development, "Take a screenshot instead of suspending". I don't know if this is standard Android or something peculiar to the Archos.