What option did you set in lilo?
You can set:
vga = ask
to test what modes are suitable for your screen (it will give you a list of options to choose from) and than just set:
vga = number
Pretty much every time I would log out of X, my resolution for the console would be all messed up.
if it helps ... if not, there is always setfont command to fix that problem (man setfont !!!)