The software on the web site is the complete package, same as what you would purchase. The software will simply not work to transmit DMX-512 signalling without the MyDMX dongle. Likewise, another cool feature for those like me who HAVE purchased the software allows for "demo mode" use to off-line create light shows. Come showtime, plug in the dongle and there ya go!
OK, as far as where the editor lives, Jingls was off by a tiny bit.
In my case, it is at:
This came FROM the web site downloadable.
Yes, it makes sense to be in the C:\MyDMX\ScanLibrary\ directory, but that's the location of the library, not the library editor.
Enjoy. What I'd do is get in touch with someone like Jingles after you've made your new fixture library item, and have him "proof read" it. In my case, he pointed out some "overkill" things I didn't really need to to. All I'm going to say is the profiles I made for my fixtures work just fine, and I'm appreciative for the help I received, no matter how small it was.