How to set a palette, a 16 color palette?

16 color palette, which includes semitransparent pixels and black and white - HOW can I set it for the work space? I need to make a certain image with those colors only - but converting a photographic image into that 16 color palette is beyond me. Can you help me please?

I'm using Photoshop 7.0 and honestly, never had to set a palette before.

Thanks for your time and answer (I hope I get one).

Joseph.

Set the image mode to Indexed color. You can set the palette depth in Save for Web. I'm not sure about how you can deal with the semi-transparent issue, since GIF only allows total transparency. It would be possible to go to black, white and 14 levels of grey, if that would work.

What is the eventual use of the image?