I got Halion One with a Cubase disk included with a Yamaha instrument.  I don't like Cubase but I would like to use Halion One with Music Creator.  Is is possible?  How would I add it so it shows up as a synth to insert?

It may be possible. 
 
Install both MC5 and the Cubase software if Halion installs with the cubase daw.  If you have the option just to install H1, select that. If not do the full Cubase install.
 
Search the cubase directory for the synths and locate the Halion DLL file. remember where it was located.
 
Open MC5 and navigate to the PLUG IN MANAGER.  Use this function to add the path to the H1 DLL file into the MC5 plug in scan list.  Run the scan when it has been added.  Now, close the plug in manager. I would restart MC5 at this point. Once it's running, choose "Insert Synth" and see if H1 is now showing in the list of available synths. If you did the "add plug in" correctly it should be there.  Try running it.
 
 

Thanks GuitarHacker
I had tried that method but hadn't reloaded MC.  When I did it your way the syn showed up but still wouldn't work.  When I tried to load a Halion bank or sound I got an error message.  So I went back to Cubase and listened to the Halion presets and decided there was nothing there a good as what I already had with the Plogue SFZ.  But you know...you always have to look for the best.

Yes... I have seen that happen. It may be the code or the drivers or something else but the synth that works in on doesn't work in the other.
 
I used to get every free synth I could find and sound fonts too. I found that many of them simply didn't work in MC no matter what I did.
 
My philosophy now is to simply get a few good synths that do work and have the sounds I want, like and need and use them and not worry about every possible sound..... and that is what I have and use.  BTW: If you buy a synth it will work..... it's the freebies and the LE versions that are often not stable and give problems. I've never bought a synth or FX that did not function perfectly.