A client recently struggled when his XP workstation's left pane disappeared. This pane contains commons tasks such as emailing files.

A simple registry modficiaton was needed to remediate the issue:

Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced]
"WebView"=dword:00000001
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"ClassicShell"=dword:00000000

After applying the fix, I killed the explorer.exe process, then re-opened it. The pane was now visible.