Yeah... I was lucky and downloaded it at work today.
As for paritions, I recommend a 20GB or bigger partition. I've got an 80GB HD and will partition it as 50GB for MCE (and all the apps I need) and 30GB (or really 25 because of the stupid rounding) for playing around with Vista.
Yes, you should have a second partition, and I would install MCE before Vista, so the boot manager from Vista can work properly...