Hi,
First, TopoFusion can use com ports greater than Com 4. I know of several users who use a USB->Serial spoofer as you are trying to do. Unfortunately, it does seem to be hit and miss sometimes, due to flakeness in the USB->Serial conversion.
None of the GPS functionality is limited in the demo. The only limitations are the Demo tiles and the limit of 3 files open. So it should work just fine.
I don't know a way to test if the GPS is there or not using HyperTerminal, except that it shouldn't give you a port error if you talk to it. If you send something to it and you get a write or read error then you know it's not correctly hooked up. Could be anything from a broken cable to software (windows) issues.
I'd give the USB-Serial thing another try using TopoFusion.
Let us know how it goes.