As quack quixote pointed out, the Kernel Framebuffer is used to draw the screen if no X is started. You can set the size using the boot-parameter vga
(deprecated) or gfxpayload
(newer).
vga=vgamodeHere gfxpayload=1440x900x32
These options need to be set via a boot option, so you'll have to edit /boot/grub/menu.lst
for Grub1, and for Grub2 /etc/default/grub
and add this boot option to the kernel.