Whatever you do, don't take the drives out of your current box and put them somewhere else, you will probably loose all your data, not all nas enclosures use the same file structures

Just thought you could also rescue an old PC, and install a couple of IDE or SATA PCI cards in there, beef up the power supply and install up to 8 drives in there. There's a standalone utility called NASLite (http://www.serverelements.com/naslite-2-hdd.php) which may well do what you need. Sort of home-made windows home server.