I have the Helvetica Regular, Bold, BoldItalic, and Italic ttf's working in my publish, however I wish to have Tahoma available as well. In the windows fonts, only Tahoma and Tahoma bold are available. Is there the other variations around?

As far as I'm aware the Tahoma font only has normal and bold faces, as it was originally intended to be a font used in user-interfaces where no italics were required. The Verdana and Arial fonts are similar sans-serif fonts that do have italics.