Greenie,
It looks like you tried this tutorial before, but did you register the DLLs in this order?
Windows Sidebar - Gadget Not Displayed Correctly
I have heard that if it is a XML problem, then sometimes resetting IE7 can fix the problem as well. It could be worth a try.
Internet Explorer - Reset
Other than that, I can only suggest a System Restore with a restore point dated before the problem.
Hope this helps,
Shawn