In my version (7.5.11.9) there is only an "options" button, and the drop down menu only has "settings" that opens in a new window - there is no "view" anywhere, and no window for selecting (unchecking) "group ims". I am totally stumped...
Open an IM window like you are having a conversation with someone. In the top right corner it says OPTIONS. Click it once and a menu will drop down and mouse over VIEW. Then uncheck the option GROUP IMS IN ONE WINDOW. Voila!