Hey Ignacio,
I figured you'd get a bunch of replies with links ... sorry I didn't reply earlier.
I can send (maybe post) a dutching calculator (Excel) for anyone who wants one. I'll clean it up, and make sure everything is working. Do you want a 2 horse, 3 horse or 4 horse version ? Actually in the 4 horse version or 3 horse version you can just set the (imaginary) odds on a runner you don't really want to a very high number , and it won't even compute, basically. Also there are free ones online.
Cheers.