OK, here's what you do to get the old icons back:
1) Copy the start menu folder to your computer (from \windows\start menu).
2) Drag'n'Drop the lnk file you want to change onto Windows' text editor.
3) For example Internet Explorer.lnk:
99#:MSPIE ?\Windows\SP_ProgramIcon.dll,-119
4) Remove everything after the ? (including the ?), so in this case:
5) Save the file and copy it back to your phone!
Samsung Galaxy S i9000 CM10.1 Nightly