Hello Bud, and welcome to Seven Forums.
In Window 7, all Windows Explorer windows share the same size and position of whatever the last window was closed as. They do not have independant size and position settings for each one.
To do what you want, open a Windows Explorer windows, size it how you want, then close it. All Windows Explorer windows will now open like this as long as you close them with the same size. Installed 3rd party program windows will have to be done one by one to have them be remembered though.
Hope this helps,