>>>Can we display superscript, subscript text in the Rich Text Box. If so how ? Can we set up command buttons for this purpose ?
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>>No. Superscript and subscript are not supported by RTF ActiveX control.
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>
>Do you know of any third party activex control that supports them ?

TX Text control, but it seems to be too expensive.
Subscripts and subscripts are supported in HTML, so you can use Web Browser control for viewing. IE5.0 and higher provides HTML editing functionality, which can be enabled by designMode property of Document object:

oleWebBrowser.Document.DesignMode = "On"

HTML editor command IDM_SUBSCRIPT and IDM_SUPERSCRIPT are not currently supported, but IMO you can use IDM_FONT command to open font dialog box and change font for current selection.

Alexander