I remember that the wwf 6.x have a file to make it ... and you musted, on the images folder and other that not remember now, put the files that make the skin.
The code for this file is
<form name="jump">
<div align="right">
<span class="tiHeading" width="100%">Choose Theme:</span>
<select name="menu" onChange="location=document.jump.menu.options[document.jump.menu.selectedIndex].value;" value="Go">
<option value="default.asp?Skin=Default" <% If strThemeSelect = "Default" or strThemeSelect = "" Then Response.Write("selected")%>>Default</option>
<option value="default.asp?Skin=DarkGrey" <% If strThemeSelect = "DarkGrey" Then Response.Write("selected")%>>Dark Grey</option>
<option value="default.asp?Skin=WinXP" <% If strThemeSelect = "WinXP" Then Response.Write("selected")%>>WinXP</option>
<option value="default.asp?Skin=IceBlue" <% If strThemeSelect = "IceBlue" Then Response.Write("selected")%>>Icey Blue</option>
<option value="default.asp?Skin=MadDogs" <% If strThemeSelect = "MadDogs" Then Response.Write("selected")%>>Dark Blue</option>
</select>
</div>
</form>
And the name was themes.inc, but i dont know who make it with wwf 7.0 becose change all the system to skin 