Yes, I have. My primary drive was partitioned C for system and F: for data including MY Documents". My two iTunes folders and libraries were in F: /My Documents/My Music.
The system partition was formatted and I installed the 64 bit version of i Tunes. I kept my old filing system on the F: Drive (not formatted) and i Tunes worked fine. I have two accounts, two libraries and 3 iPods in use by various grandchildren etc. As a back up I use FreeFileSynch to keep a mirror image of "My Documents" on an external drive as well as an ATI image, so you could use that if you wished (or even a normal copy of your i Tunes folder) so you could simpy re - import it to the new arrangememt.No probs with DRM etc - in any case you are allowed up to 5 computers in i Tunes. I think I had to authorise an apparently new computer when the new i Tunes started.THe programme files for iTunes are seperate from the data.JB