System hangs - OLE, COM, or DDE?

My Windows XP Pro SP2 suffers from bizarre, consistent 8-second delays
whenever I try to:

* launch a registered application by clicking a document in windows
explorer
* launch a registered browser by clicking a link anywhere in Windows
* launch an application using a shell keyboard shortcut (the Ctrl+Alt+
[?] ones).

Always this delay, on top of whatever time it takes to launch the app
or perform the command.
Any ideas?