The easiest way would probably be to re-use <DIV EDITABLE="TRUE"> behavior
or to start off DHTML Editor SDK (actually, both seem to use the same
ActiveX control behind the scenes).
The rest is mainly lots of JavaScript playing with the DHTML Editor API to
make text bold, in italics etc.
Of course this will work only in IE, but I really doubt if this could be
implemented at all in browsers like Netscape 4.x
