There is always a way! Here is one of them.

1.) Make a copy /dotnetnuke/images/help.gif
2.) Change /dotnetnuke/images/help.gif to a completely transparent gif file
     Note: this will change the icon for all of you sites
3.) Change your containers were the action button is located.

I change my container by adding the text in red:
<TD valign="middle" nowrap><dnn:VISIBILITY runat="server" id="dnnVISIBILITY" /></TD><TD><DIV class="ActionButton_Help"><dnn:ACTIONBUTTON5 runat="server" id="dnnACTIONBUTTON5" CommandName="ModuleHelp.Action" DisplayIcon="True" DisplayLink="False" /></DIV></TD>

We know have an action button that uses a transparent gif to launch the help file.

4.) Add a line to your portal.css file to get what looks like the help file icon back. Usingthe copy of the help.gif file we created.
DIV.ActionButton_Help {background-image:url(help.gif)}
The background image of the DIV tag will be the icon help.gif. When viewed by the user of your website it will look like the the opriginal image.

5.) Now anytime you want to use a different icon for the help file, you simple add DIV.ActionButton_Help {background-image:url(help.gif)} to your skin.css and change the icon to whatever you like.

Note: You will have to play around with the SIZE of the image and NOREPEAT options on the background ect. but I believe you get the idea.

I just made this work on my tet site.

Anything is possible!
Tom