I used to get similar error..while closing.. memory at ( some HEX no) could not be refrenced... WTF.

You are stuck with a bad OS and a Bad browser. Start Working with Firefox.

Check for all viruses,spywares, adwares.
Do you rember installing anyting ? ( might cause conflict)
Make sure you have all the essential Processess running.
BTW, try to uninstall just IE and Reinstall... ( if thats a possibility in vista)
Also, does Vista has System Restore ? Try that before you thing abt reinstalling the OS.

P.S Firefox is the most awesomest-test Browser :D