You could do this if you want. I personally prefer a main drive(boot, games, whatever) and an external backup drive(zip files, photo archive, etc...) No harddrive is full proof, so I always make backups of stuff I REALLY want on CDs/DVDs
As for partitioning, that's a yes/no answer. Logically, it'll be the same(two different drives) If your windows partition goes out, you still have your storage partition. However, if something goes wrong with your hardware on your HD, you loose both partitions.
Also, having a partition would be a bit slower anytime you try to access something from both partitions. Say you install a game, part it has to load crap from the windows dir or something for DirectX and the other has to load from the storage partition. The heads have to jump back and forth between partitions making it that much slower. Probably nothing major, but I feel sure two drives would be faster.