System Crashes

My PC is Dimension 4600, running Windows XP Service Pack 2. Recently I have had a series of system crashes when Windows closes down and the screen is filled with a blue error message entitled IRQL NOT LESS OR EQUAL. The MS crash analysis idicates an error caused by a device driver but looking at device manager does not show any conflicts. The only recent change is to install MS Money 2005 in place of Money 2004. The only other factor could be when closing Windows I get the message "Vsmon.exe.dll" initiation failed. But Windows continues to close. Any ideas, please.