this is how i did it in MDK10.0, so it should work in 9.2 also............
go to ~/.kde/share/icons/ this is where your user installed icon themes are installed.
choose the folder of the icon theme that you are using, or that you want to use. (the default KDE icon theme is Crystal)
go into the size folders (16x16, 32x32, etc), then into the apps folder. the 2 most common are 32x32 and 48x48
find the icon named kmenu.png and rename it to menuk-mdk.png
now, reload your icon theme (K menu -> System -> Configuration -> KDE -> LookNFeel -> Icons, select a new theme, then your original theme and click apply). you can also use any .png file to make an icon, provided it meets the size requirements (IE: 16x16, 32x32, etc.).
you should be all set now. you should have a new menu icon. using this method, you should be able to select any icon you want to be your new K-Menu icon.