When you try to have SysInternals’s Process Explorer (procexp.exe) replace the Task Manager on Windows 7, it won’t work out of the box. The new task manager cannot be found (as you will see when trying to start the task manager from the task bar), because the file procexp64.exe that Process Explorer creates to be instantiated when you start the task manager gets put in a temporary directory under your user account, and is inaccessible. The solution comes in two parts:

• Find procexp64.exe which gets placed in C:\Users\YourUserName\AppData\Local\Temp. Copy it to your Process Explorer installation directory.
• The registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\taskmgr.exe holds the path to the current taskmanager. Edit this key to point to the new location of procexp64.exe.

Good to go!