Those firmware files allow you to flash a fresh* install onto your device, it's all you need really. Aside from hardware failures (especially the USB port, about which search the forum/wiki), this device is unbrickable if you have the flasher and the firmware. The wiki** has a great guide here (and it even mentions Windows 7 so your other issue might be answered there). For backing up existing installs the excellent BackupMenu will let you create images of your RootFS onto your MyDocs partition or SD Card. *Ideally you'll want to start work of a fresh install to be certain there's nothing malicious on there from a previous owner. **n900 users are so fortunate to have such a comprehensive wiki and this forum has nearly every question you could ask about it answered 5 times over . I highly recommend you read through the beginner and power user topics on the wiki