The easiest solution would be to use the description field, which is already html.
if you can't use that then you can create a custom field
http://nbsdocs.nbrightproject.org/Documentation/Developerguide/CustomFields.aspx
Look at the current templates to see how the product description is done, you'll also need to use the htmlof tag to display it.
The other way is to alter the product admin template to change the summary field to a html field, but remember to update the display tag token to a htmlof tag. (NOTE: create a bespoke template at the portal level to avoid your changes being over written by any upgrade., http://nbsdocs.nbrightproject.org/Documentation/Integratorguide/Themes.aspx )
if you can't use that then you can create a custom field
http://nbsdocs.nbrightproject.org/Documentation/Developerguide/CustomFields.aspx
Look at the current templates to see how the product description is done, you'll also need to use the htmlof tag to display it.
The other way is to alter the product admin template to change the summary field to a html field, but remember to update the display tag token to a htmlof tag. (NOTE: create a bespoke template at the portal level to avoid your changes being over written by any upgrade., http://nbsdocs.nbrightproject.org/Documentation/Integratorguide/Themes.aspx )