Lucas recruited Tartakovsky (sp?) to create the Clone Wars animated. That would make it canon to me. Plus, this is how Lucas plans to tell the Clone Wars story that falls between AOTC and ROTS. I think he's going to try to avoid as much Clone Wars information as possible in ROTS. So you'll want to watch this series for it all to make sense.

And, yes, Clone Wars volume 1 comes out on DVD on 3/22, the same day as the reissues of TPM and AOTC. And I think season 2 of Clone Wars comes out on Cartoon Network somewhere around that time, too.