I have one such virtual machine, and I hadn't realized sharing it was even an option. Not a bad idea at all!
However, not having foreseen such a use, I created it with static allocation of a virtual 8 Gb disk, and also created a snapshot right after finishing the initial update. It now occupies 13 Gb, which I believe is too big a torrent for this purpose.
But would this work? Are VMWare images shareable and crossplatform? I created mine under (surprise, surprise) Ubuntu 6.10.