I just replaced the AA gun on strategy map and showing white square around it, although it would be alpha transparent, so i add it and have no effect. Have anyone manage to get around this?
What do you want us to say? You did something wrong.
Upload the pic you changed and we can take a look but a vague description of a problem is really hard to diagnose from afar, especially when it relates to graphics where a wrong index can screw up everything.
as the attached image is an png (probably converted by the forum?) I'm not sure whats wrong with the bmp you created, but it's not actually hard to get it working and i attached a fixed bmp for you.
Easiest way is to open the old, working icon in gimp.
Then just move your new icon on top of it, merge the new layer onto the old one and save the icon, so that no indexchanges occur.