Hi Robert, thanks for your help.
By using the boot code: base norestore xvesa=800x600x24 , I can successfully boot TCL 2.8 with 800x600 resolution.
However, when I use the boot code in the kernel line:
kernel /boot/bzImage quiet xvesa=800x600x24, I still can't boot with 800x600 which I haven't any problem in TCL 2.7.