Basic NAS - any security?

Does anybody use a basic form of NAS out there with file security on it.

My very useful USB-drive home-made NAS works a treat apart from there being
no user security which I'd like to implement (as on a wi-fi enable lan)
- driven off the samba built-in server - but I can't enable controlled file
sharing or any form of locking I know of.

Few accesses, not for (secure) backup but file access across different
machines on at different times/alternate copy of files.
Mix of win98/xp.

I'm trying to avoid a separate box with permanently running harddrives &
PSUs & fans etc.

No need for raid (any), hot swapping drives, large drives. Useful if
honours dhcp (any class range) but can give fix ip no prob.

 

The buffalo linkstation ticks all the boxes I think. You can set up
users who can or cannot access any shared folders on the device. For
example if you set up 3 shares, you could grant user A full access to
all 3 folders, user b read-only access and user C can only access share2
etc.