Hugh's GIF Toolmake transparent GIFs
Download Hugh's Gif Tool from Winsite
Although the program is very useful and does its job correctly, the user interface is a little deceiving; just remember to specify your input and output files using the select buttons and not the text boxes. The text boxes in those sections are just there to indicate what you've selected, which is redundant since it's listed again in the summary section.
There's another minor trouble spot with Hugh's GIF Tool: the program will not let you overwrite the original file, even if you've chosen to make a backup of it. There is only an obscure warning that the input and output files are the same, and when you try to transparentize the file, nothing happens. So be sure to name your output file something different from the source file.
Still, clear instructions are included, and with this extra advice, things should go smoothly.