Tips For Debian on Agestar
Chris (Whites11) and several others have pointed that the source code for a device similar to Agestar have been released by a German company (http://www.multicase.de/en/products/76/ns348s.html). I have not looked carefully at the source code of this one, but none of the people on the mailing list have got it working with networking enabled.
Kari Ahtiala who owned several NAS devices (SLUG, NCB3AST, NCH3AHT), said that you can just move your disk from NSLU (SLUG) to Agestar just fine: