Well, I've had my ZP 450 working now for quite a while. It works with PayPal, Open Office, Endicia, Dazzle, and Shipworks. I'm not sure about UPS Worldship but I don't have a need for it right now.
If I remember correctly, using windows print management under administrative tools was the key. There were about 15 different driver
installs from my previous attempts, which was clearing causing conflicts. I also had a few extra duplicate printer installs from previous attempts that needed troubleshooting.
I think those two issues were the main reasons behind my troubles. I simply removed everything and wiped out all the drivers
that I could.
Another thing I might add that seemed to help was not connecting the printer until prompted. Connecting it in advance causes windows to install its own drivers, or at least try to, which corrupts the zebra drivers I'm guessing.