There isn't a convenient way to turn them all off, but you can use the techniques shown in this tutorial:

Troubleshooting DotNetNuke Skins

to make them disappear.

hello,

Even using those techniques, there is not a simple way to remove the help?  using CSS. 

Each help?  Has its own unique ID, so the only way I have found to remove them all using CSS is the following code:

.SubHead img
{
display: none;
}

This will remove the help?  From the host menu/host settings page

But it will also remove any images that are within the subhead class which may cause problems in other areas, so you may want to just create an admin skin which uses this CSS code and then double check the rest of your site to ensure no other images accidentally removed.

Hope this helps,

Thanks,