What you need;
sudo aptitude install davfs2 -y
This will get DAV file system being enabled.
Later, what you could do is to put your details in davfs configuration file, located at /etc/davfs2/secret
Next, you need to mount the box.net through davfs using mount command.
You can put inside your etc/fstab too, but I found out the system will complain it cannot mount the filesytem (heck, you need to connected to network before you can mount. Wireless connection usually only being enable when you already reached your desktop interface). So I suggest you simply use the command line mount command:
Create mount location first;
sudo mkdir /media/box.net
A bit lengthy, you could paste this to a file, let say mountboxnet.sh and chmod +x, execute by ./mountboxnet.sh later on:
sudo mount https://www.box.net/dav -t davfs /media/box.net
You can also find someone else blogged the methods of accessing box.net WebDAV by using nautilus, which is fairly simple too. But I prefer the CLI way :)