Are you talking about a splash screen for grub-0.97-splash?
The image has to be 640x480, 14 colors max, saved in xpm format and then gzipped. On the Gimp menu, use
Image | Mode | Indexed
select "Generate optimum palette and set maximum number of colors to 14.
The grub line is something like this:
splashimage=(hd0,0)/boot/grub/tc_3.4.1_lem_splash_14.xpm.gz
I tried to upload an example but got a message indicating upload directory is full. Probably just as well, as the TC wallpaper/logo looks like crap in that format (needs more than 14 colors).