TrustedReviews have looked at the ZyXEL NSA-2400 NAS appliance

The NSA-2400 is equipped with a decent 1.3GHz Via C3 processor although this is only teamed up with 128MB of memory, which cannot be upgraded. You get a single Gigabit Ethernet port and a pair of USB 2.0 ports at the rear with a third USB port on the front panel. All three USB ports can be used for connecting external storage devices but the appliance doesn’t support sharing USB printers. On connection a USB device is automatically shared on the network with NTFS file systems restricted to read-only.

ZyXEL NSA-2400 NAS appliance Review