Hello,
right click the download folder in your account,choose properties,choose the location tab and you'll see where it's stored now.Recreate a similar folder on the other drive like "D:\Users\"
Your Name"\Downloads" and then go back to the location tab click "move" (not sure->translation) and search that new folder and choose it and apply so the downloads get to the new folder on the other drive.
You can do the same with your music/video/documents/images folders if necessary.
Make sure you create that new folder on the other drive and point to it,so not just pointing to the new driveletter!
A video from ncis techtips in which it's explained too,but he uses more general folders,
http://www.youtube.com/watch?v=qMo8krAJd5Q
it...