I have a laptop with x2 hard drives: C and D. When I set up my computer, I only had a few GB of music so most things went on C and D is pretty empty. I want to move all my iTunes music, videos etc to the D drive, but I want this to work seemlessly, no missing links etc.

What's the most straightforward way? Can I just copy my iTunes folder, delete the original and change the iTunes media folder location in preferences?

http://discussions.apple.com/category.jspa?categoryID=149

Even easier than that. Assuming you're on Windows, follow this:

http://support.apple.com/kb/HT1364

Doing what you describe can lose ratings, playcounts, etc – doing it the way above should keep it all intact.