If it were me...I'd be sure to have a drive large enough to partition mutiple file systems, FAT/32, NTFS and even 'nix file systems as Dell is now offering pcs/books with Ubuntu installed.
I would recommend a NAS, such as a Thecus N2100 or N299. Then you don't have to worry about which OS,is running on the client computer. In an office environment you can backup several machines at the same time.