Found at WinGuides.com. As always, backup the registry before making any changes.
This setting specifies whether a new process is created for each instance of Internet Explorer that you start. This can prevent one instance of Explorer from affecting other instances if it stops responding.
Open your registry and find the key below.
Value Name: BrowseNewProcess
Data Type: REG_SZ (String Value)
Value Data: Yes or No
You may need to create the key if it does not already exist.
Create a new String value, or modify the existing value, called 'BrowseNewProcess' and edit the value according to the settings below.
Exit your registry, you may need to restart or log out of Windows for the change to take effect.
Note: Normally this is automatically enabled or disabled based on the amount of random access memory (RAM) that is installed in the computer. If the computer has less than 32 megabytes (MBs) of RAM installed, this setting is disabled. If there is 32 MBs of RAM or more installed on the computer, the setting is enabled.