I use VMWare Fusion on my Mac for when I need to use another OS (personal preference - I just prefer it to Parallels). As far as the Sony goes I used it to register the device, and also to download books that refuse to download in any browser other than IE.
But I then lob the books onto my Mac partition, and shove them on the reader using Calibre
Can't comment about the firmware update side of things, never done it...