This is a trick I learned on the old old forum, but the original post is inaccessible now. Blurymind asked for a HOWTO, and since I didn't feel like doing any of the things I had to do I decided to write this HOWTO instead. I'll assume you're using the Gimp.
Disclaimer:There are multiple ways to do this, I can't guarantee this is the best way or will work for you. It worked fine for me though. I am not responsible for any damage resulting from you trying to follow this HOWTO.
1) Get yourself a nice picture. 2) convert it to 640x480lilo only supports 640x480 bitmaps with 16 or 256 colors. So make yourself one with the gimp or something like that. To make sure it'll still look as pretty as it gets with 256 colors, set "image -> mode" to "Indexed".
choose "Use optimum palette" so it will create the optimum palette for that particular picture. Save the picture, it should be about 310 KB.
3) copy the picture to /boot/bitmap/
4) create an accompanying .dat file here's where it gets interesting. Every image can use it's own .dat file.
It should have the same name as the bitmap, except that it's called .dat instead of .bmp.
In it, you define the look and placement of the menu and the countdown timer.
It should contain at least:
bmp-table=<x>,<y>,<ncol>,<nrow>,<xsep>,<spill> (location and size info of the table)
bmp-colors=<fg>,<bg>,<sh>,<hfg>,<hbg>,<hsh> (foreground, background,shadow and highlighted colors for table)
bmp-timer=<x>,<y>,<fg>,<bg>,<sh> (location and colors of countdown timer)
The colors are the same colors as in the indexed picture. So, if you want to use black, you'd use the "color picker" and pick black. It'll show a screen with some info

Here you can see, that the color I picked is nr. 4. (and it's not pitchblack).
For more info about these options check out "man lilo.conf" and "man lilo".
Now, my file looks like this:
#timer is close to the top right of the bmp. no value for background=transparent
bmp-timer=540p,20p,253,,111,
#table starts 20 pixels down and 20 right of the topleft
#only 1 column is used.
bmp-table=20p,20p,1,10,,
bmp-colors=209,,65,254,,209
5) Make sure the new image and the accompanying .dat file are usedNow, we have to include this info INSIDE THE IMAGE! We can do this with
lilo -E filename.dat
Now, remove the old boot.bmp (it's a symlink to another bitmap), and link it to your new one:
rm /boot/bitmap/boot.bmp
ln -s filename.bmp /boot/bitmap/boot.bmp
now, update lilo:
lilo -v
reboot and check it out!