Mspaint created icons in XP

All icons lovingly created with MSpaint (for Win98) (32x32 .bmp) appear in XP with background (previously transparent) now solid black. I've obviously tried everything I can think of to sort this: Display is as before (Matrox 32 bit, 1280x1024), Scheme is Windows Standard. All other colours are OK, and floodfilling background with any colour, or even black, does just that. Have worked my way thru reasonable tweaks and now need a guru, or possibly "black" magic.

 

Open the BMP file in an icon editor and specify the transparency color. For example, using GIF Movie Gear, go to Frame > Global Properties > Transparent and select the background color. Then save as ICO.