microB is the name of the webbrowser on the n800. It's based on the gecko engine which is the same engine that firefox uses. There's also a port in progress of the "full" firefox web browser at the moment, but it has a long ways to go.

You can use just the regular n800 file manager to copy files from smb (i.e. windows) shares, or any upnp devices on the network. The quicker way to do it is to plug the n800 into the PC using the USB cable and copy the files over.

When you plug your n800 into your PC, the n800 becomes nothing more than an over-glorified card reader, and you can just drag and drop files via windows explorer like you could to any other SD card.