rendertweening

When I take the program off debug mode the models flicker back and forth as they move,
when I enable debug everything is fine and smooth when using rendertweening.

Try this:
http://www.blitzcoder.com/cgi-bin/articles/show_article.pl?f=johnblackledge09202003161847.html

yep thats the article I based my code on (or ripped the code from)

Then go looking for another explanation.
I've been using this code for over a year, and anyway it's based on Mark's Castle Demo, just a little more verbose so it's easier to understand.