Here is a copy of my registry based on another fix I found at these sites.
http://windowsxp.mvps.org/samewindow.htm
http://forum.notebookreview.com/windows-os-software/53378-explorer-opening-each-folder-new-window-cant-change.html
They're based on Windows XP, so I copied mine to reflect Win7 x64 (Home Premium). You can bump your values to mine, or copy the code into notepad, save as a .reg file, and merge with your own registry (make a backup first). Reboot after the merge for any changed values to take effect.
;--------------------------------------------
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\Folder\shell]
[HKEY_CLASSES_ROOT\Folder\shell\explore]
"MultiSelectModel"="Document"
"ProgrammaticAccessOnly"=""
"LaunchExplorerFlags"=dword:00000018
[HKEY_CLASSES_ROOT\Folder\shell\explore\command]
"DelegateExecute"="{11dbb47c-a525-400b-9e80-a54615a090c0}"
[HKEY_CLASSES_ROOT\Folder\shell\open]
"MultiSelectModel"="Document"
[HKEY_CLASSES_ROOT\Folder\shell\open\command]
"DelegateExecute"="{11dbb47c-a525-400b-9e80-a54615a090c0}"
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,45,00,78,00,70,00,6c,00,6f,00,72,00,65,00,72,00,2e,00,65,00,78,00,\
65,00,00,00
[HKEY_CLASSES_ROOT\Folder\shell\opennewprocess]
"MUIVerb"="@shell32.dll,-8518"
"MultiSelectModel"="Document"
"Extended"=""
"LaunchExplorerFlags"=dword:00000003
"ExplorerHost"="{ceff45ee-c862-41de-aee2-a022c81eda92}"
[HKEY_CLASSES_ROOT\Folder\shell\opennewprocess\command]
"DelegateExecute"="{11dbb47c-a525-400b-9e80-a54615a090c0}"
[HKEY_CLASSES_ROOT\Folder\shell\opennewwindow]
"MUIVerb"="@shell32.dll,-8517"
"MultiSelectModel"="Document"
"OnlyInBrowserWindow"=""
"LaunchExplorerFlags"=dword:00000001
[HKEY_CLASSES_ROOT\Folder\shell\opennewwindow\command]
"DelegateExecute"="{11dbb47c-a525-400b-9e80-a54615a090c0}"
[HKEY_CLASSES_ROOT\Directory\shell]
@="none"
[HKEY_CLASSES_ROOT\Directory\shell\cmd\command]
@="cmd.exe /s /k pushd \"%V\""
;--------------------------------------------