I haven't done this but I have heard that when you buy the actual ArchiCAD the trial version automatically switches to 'full' version and the files you created in the trial version will be converted to your new 'full' ArchiCAD files. But this only works if you are using the same computer for both the trial and full version. Hope that helps!
I was able to open the trial version files on the original computer then save them using the full version. After that they could go from comp to comp.
How the trial version works is that every trial installation has its own unique file format, sorry that's as far as my knowledge goes!
Yes you definitely can. Basically when you open the file in the full version it does a one time conversion, which means if you save you can no longer use it again with the trial version.