(Applicable to all versions of Expression Web.)
Expression Web comes with three preconfigured font family groups. They are:
- Arial, Helvetica, sans-serif
- TimesNew Roman, Times, serif
- Courier New, Courier monospace
In this tutorial we will add a third.
Font Families Tab
To launch reach the Font Families tab where you can add or remove font family groups you must first launch the Page Editors Options dialog box using Tools > Page Editor Options. From there select the Font Families tab. (Alternatively, you could use the (Default Font) dropdown on the Format toolbar.)When you first launch it will look like:

New Font Family group should be selected by default. If it is not, select it now. Move you mouse to the textbox to the left of the "Add" button. (The Add button will be grayed out until you have a font name in the textbox.)
Start typing "Tahoma" and you the listbox should jump to it as you type.

Now the Add button will be active, use it then type in "Helvetica" because this is a Mac font you are not likely to have it installed on your system so you will need to type the whole font name, again use the Add button. I recommend putting Helvetica before adding Arial since most Mac users consider it to be more attractive than Arial. Continue adding "Arial" then sans-serif. Remember that you must use the Add button after every font.
When you see the complete list of font families ending with the generic sans-serif either select the (New Font Family) option or use the Okay button at the bottom of the dialog box to close the Page Editor Options dialog box.

Your new font family group will now be available in the New Styles, Modify Styles dialog boxes and in the Format toolbar's font dropdown