I am big fan of having big icons. Some of them scale, but some does't. Why? How to repair this? What replacement should I search for?
In XP application icons were only required to be made up to 48x48 pixels. If I remember correctly, Win2000 and before only used icons up to 32x32 pixels.
With the introduction of Aero, with Vista, icon sizes went up to increased to 256x256 pixels.
If you really wanted to replace your older application's icons with fully scalable ones, you will have to open the application .exe file with Resource Hacker or XN Resource Editor, and replace the icons.