So far I had "designed" my app-icon in the Visual-Studio-Editor. 16-Colors, 4kB. Now someone created a more sophisticated and up-to-date app-icon for me, which results in a filesize of about 250kB.
Problem: A user reported, that win2000 is complaining, because it is not able to digest this amount of data for an icon.
Question: What can be regarded as best practice for application-icons. In detail: which resolutions and which color-depth-variations should be contained in an icon?
In general I wouldn't care about Windows 2000 any more as even Microsoft has begun to stop support for it. For Windows XP this article on MSDN might help you.
I'd say best practise would be to follow the icon example Microsoft is setting with XP and Vista icons. It's so rare to see anything less than 256 colour icons these days, that when I do see them I think the program is quaint and outdated. Perhaps best bet is to wait for Microsoft to add SVG icon support; perhaps in Windows 7, if we're lucky?
I've always tried to stick to the following set of sizes to get a reasonable icon on most systems.
This produces an icon of about 35KB in size and seems to work on systems from win95/98 all the way up to Vista. I still develop on a Win2000 machine and these work just fine.
icoFX is a free icon editor which I just found. It seems to work nicely - you just check the boxes for the formats you want "slaved" to your big 256x256 icon which is the one you edit. Searching stack overflow for icoFX - others agree.