XP saves the exact window size for IE on exit, but only if you do not have it maximized. It does remember if you had it maximized or not, but only for some windows as you are aware.
These steps should work for any version of IE, including IE7:
1) Close all open IE windows.
2) Change your IE shortcut settings back to opening in a normal window.
3) Open IE and, if maximized, un-maximize it.
4) Resize the window to whatever you would like it to be.
5) Do not maximize. Close the resized window.
6) Open up IE and your window size should have been preserved.
7) Maximized IE and close it.
IE should now open maximized, and any windows that do not should be the size you set when you resized the window.
