Hey Mildred, I ran into this same problem... Where the editors were on macs... I eventually used this workflow:
I ended up exporting my graphics using the Xpression AVI..
Then I would use Adobe Video Encoder to batch convert all the XPression AVI into Quicktime Animations. I know it's an additional step in the workflow, but it worked really well for me & the editors. You may want to ask your editors if they know of a cheap Video Conversion Program that you can use; if you don't have access to Adobe Video Encoder.
Steve
#XPression