On my SLES 11 I tried to change grub splash screen, by editing following line in menu.lst:

gfxmenu (hd0,0)/message

I change "message" file with my custom picture. I tried different formats (png, tga, xpm, xpm.gz) but each time I'm getting following error:

Invalid file format

and my splash picture is not shown. I tried to pack the file using cpio, but it's no good. Can anyone please explain me:

1) in which format I should save the picture?
2) what should be the resolution of it?
3) do I need to cpio it?