The data (each Explorer window's size, position, view settings, arrange settings, etc) is stored in the following registry keys:
HKEY_CURRENT_USER\Software\Microsoft\Windows\Curre ntVersion\Explorer\Streams
HKEY_CURRENT_USER\Software\Microsoft\Windows\Curre ntVersion\Explorer\StreamMRU
You cannot edit this data, however! Delete both keys to reset it (make sure no Explorer windows are open first, though).
The above 2 keys are used in all versions of Windows (since 95/NT); Windows XP also uses the following keys, so you might want to delete these too:
HKEY_CURRENT_USER\Software\Microsoft\Windows\Shell \Bags
HKEY_CURRENT_USER\Software\Microsoft\Windows\Shell \BagMRU
HKEY_CURRENT_USER\Software\Microsoft\Windows\Shell NoRoam\Bags
HKEY_CURRENT_USER\Software\Microsoft\Windows\Shell NoRoam\BagMRU
Also, data on which groups are expanded in the 'task pane' (the pane on the left with groups like file/folder tasks, other places, details, etc) is stored in the following key:
HKEY_CURRENT_USER\Software\Microsoft\Windows\Shell NoRoam\DUIBags
Delete that to reset this data too.
Windows will only store so many of these entries before deleting old entries to make room for new ones. You can increase this value (I've no idea what the default is offhand, but it's stupidly low) using a program such as Cacheman -
http://www.outertech.com/
Also, you might like to try a program that I wrote called CleanUp, which deletes the above registry keys and various other crap that clutters up the system (IE's cache, cookies, history, etc) -
http://www.djtsoft.com/