Convert bmp to 256 colors

I need to reduce a 32bit bmp to a maximum of 256 colors, either manually or through so开发者_C百科me built in .net functionality. I haven't managed to find any info on how to do it. Could someone offer some pointers please.

Edit: To clarify, I don't really just want to convert the 32 bit bmp to an 8 bit bmp. I want to map the input bmp to a standard 256 color palette, so I know it will display ok on a portable device. A kind of "make web safe" function.