Although I've never got Fn-F3 to work on mine (Thinkpad T22), do consider compiling the enhanced Thinkpad ACPI support (ibm-acpi) into the kernel. Although it's not fully complete it works great, depending on which Thinkpad you've got. I recommend downloading the latest 2.6 kernel.
If the patches do work then /proc/acpi/ibm/* will appear, and you can edit the scripts in /etc/acpi/ to do the work.
(I can't remember the exact commands, but it's along the lines echo "lcd_off" > /proc/acpi/ibm/lcd)
By the way there is a comprehensive site to consider, where you can find lots of Linux-related information regarding Thinkpads.
The address is: http://thinkwiki.org/
And the website for the ibm-acpi module? http://ibm-acpi.sf.net/
for the Linux kernel)