Semi Noob needs help designing a solution

[selkov]

I own an  LS421DE at home and have come to rely on it a lot but have not used any of the back up features. I would like to migrate my office into a similar setup.

The needs at my office would be:

1] Six user file access from on sight hardwired desktops and four internet based lap tops.
2] Redundant backups- I would like to create a daily backup to another NAS either on sight or off sight
    And i would like to keep a months worth the daily backups.
3] Assignable user rights by login.

I am willing to consider a different NAS if the capabilities were more user friendly [I find the  LS421DE  a bit clunky when trying to assign access right. Also if it were faster that would not be a bad thing.

And lastly do any of the NAS's have the ability to run software not native to the NAS?

Thanks to all for your responses
-Eds