Reuven,
Just to be sure this detail hasn't tripped you up... tcl and the AOLserver tcl api respectively use different naming conventions for charsets.
So reading in your file on disk you'd use:
fconfigure $fd -encoding "iso8859-8"
Returning the page you'd use:
ns_return 200 "text/html; charset=iso-8859-8"
(note extra hyphen in second case).