Hey fat tire, Welcome to the forum.
There are a lot of threads on chains, alignment and such, but I'll go through it real quick for you.
FIRST, Engine is mounted STRAIGHT, TIGHT and SOLID. No movement whatsoever. NEXT, The rear sprocket is in DIRECT line with the drive sprocket with NO wobble. Even a little off will throw a chain. If these two things are done then you should be having no problems with throwing chains. Every time I've heard about someone throwing a chain it was an alignment issue. Either the alignmemt was off, or something was loose, throwing off the alignment. The last 10 or 15 posts here: http://motorbicycling.com/showthread.php?t=43415&page=6
get into some of this issue.
Again, Welcome to the site. From here do your searches and I'm sure you'll find all the answers you need.