What icon resources are most relevant to windows 8? I have currently the largest icon in res file 48x48 x256 colors, should I have a larger one for Win8?
Nothing has changed in this area, at least for desktop apps, since Vista. In other words, you are already 5 years out-of-date. ;-)
The guidelines that were introduced for Vista remain valid. For application icons the guidelines say:
Application icons and Control Panel items: The full set includes 16x16, 32x32, 48x48, and 256x256 (code scales between 32 and 256).
The 256px icon should be a compressed PNG icon. The Delphi 4 resource compiler does not support such icons. You can use, for example, the MS resource compiler, rc.exe.