Tsunpack was designed to work using default msts install paths....You have to fix the registry to point to your present msts install before you use it. READ documentation! Ottodad has an excellent Registry repair kit for doing just that...
http://www.otto-wipfel.co.uk/downloads-various/
Follow the instruction exactly! Then run your Tsunpack..
The other alternative is "apkex-v3-07.zip" from the library here...it works just as well and might be easier for you to use in case you aren't comfortable messing with registry settings...it runs independently from MSTS and will unpack your activities...a little piece of genius software...
Nothing works if you don't read the documentation!
I'm like an old SD9; It Growls, Howls & squeaks...but it will run forever!