For "portablizing" specific apps I use VMWare's ThinApp (formerly known as Thinstall). I created a clean Windows Installtion in a virtual machine and there I simply install an app before packaging it with Thinapp.
Till now I portablized apps like:
- Creative Suite 3
- Mindjet Mindmanager (uses complete .NET FW appendice)
I think everyone knows that the apps mentioned above are really complex scenarios.
And so my definitive suggestion for specific apps (respectively those more complex than a 10-File utility)is ThinApp. Give it a try.
So far, :tony