Try setting IE11 into compatibility mode, or vice-versa. There is code added to later versions of NetTalk to handle changes in IE, so that may not help, but it's worth a try.
IE has changed a _lot_ since 2006 (NT4 era) and there've been a lot of small tweaks here and there to keep things going along smoothly. Indeed browsers are changing as we go, and it pays to keep things up-to-date (if only for security reasons.)
I understand the economic issues - it always seems like these kinds of jobs are hard to get to, but sometimes it is what it is. Unfortunately the longer one puts it off, the bigger the task becomes.
cheers
Bruce