Sure, you can use any share you want.

Edit /etc/fstab (as root and on the Pi) and add a line that looks something like this:

//$ADDRESS_OF_ROUTER/volume1 /mnt/nas cifs username=$USERNAME,password=$PASSWORD,rsize=2048,wsize=4096,cache=strict 0 0

Save that, then type "mount /mnt/nas", or just reboot the Pi.