There's no such thing as a 'default drive', except that the BIOS looks in the c:-drive when looking for something it can boot from. Can you explain what you really want?
What do you mean with itunes? The program or the music files?
You can't copy a program and expect it to work. All you can do is uninstall and reinstall to a new location. If you made any non-working copies, you can safely remove them with Windows Explorer.
And you surely can delete duplicate music files with Windows Explorer. Just keep one copy to listen to in the location your music program expects them (that's somewhere in Tools>Options or equivalent, depending on the music program).
Hope this helps.
I recently had 80mg hard drive (D)added to my hp Invent with windows xp. My default drive (C) has 20mgs and is running out of space. I am certain that in trying to transfer my itunes to the D drive, I just inadvertantly made multiple copies of my itunes and made my c drive even smaller. I'd prefer to make D my default drive, since it's bigger. Can I do that? If not, can I find and delete extra copies of itunes?