I am not sure if what you are asking is what you really want. If you download purchases you will get just purchases. You won't get your playlists, or tracks from other sources, nor ratings, nor many of the other things you may asssociate with your library.
Yes, you can just download:
Downloading past purchases from the App Store, iBookstore, and iTunes Store - http://support.apple.com/kb/ht2519 - enabled with iTunes 10.3 and newer; not available in all countries; only apps, books (not audiobooks), music, and t.v. shows (not movies). Discontinued items not available. For items not included in the iCloud list, or locations or computer systems where iCloud is not (yet?) available, you only get one download per fee paid. Apple notes it is your responsibility to back up your purchases.
Select the store on the left side of iTunes.
Click on Purchased on the right side under Quick Links.
You can redownload your available previous purchases.
Alternatively you might want to move your existing collection:
iTunes: How to move your music to a new computer [or another drive] - http://support.apple.com/kb/HT4527
do not confuse moving your whole folder and library with moving just media files as in
iTunes for Mac: Moving your iTunes Media folder - http://support.apple.com/kb/HT1449
Quick answer if you let iTunes manage your music: Copy the entire iTunes folder (and in doing so all its subfolders and files) intact to the other drive. Start iTunes with the option key held down and guide it to the new location of the library.
If you have the files on iPod/iPhone, you can transfer iTunes Store or App Store purchases to your computer from your iPod, iPhone, or iPad. The computer must be http://support.apple.com/kb/HT1296 By the way, if you have non-purchased songs on iPod/iPhone, you can use this iPod transfer program. It help you to transfer songs/videos/photos etc from iPhone to iTunes.with the used to purchase the items. Please refer
Hope it helps.
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