I just tested it, and it works fine, but it might be that the RTF box, that comes with VB5 doesn't support RTF 1.6.
There might be usercontrols out there, that can do it for you. That is my only other solution.
You could however also see Microsofts homepage under RTF documentation, it might tell you which version the vb5 control supports, and then you can just alter the code so it works with the older version.
I have included a small test project, which works.