Shortly after getting the new laptop, which came with 10.4 installed, I did an erase and install of 10.5. Shortly after doing this, I noticed the keyboard started freezing, while the touchpad and button worked just fine. “Oh no”, I thought, this is where I come to regret getting the refurb. But a little digging around found an article at MacFixIt.com. One of the posters suggested the following command:

sudo update_prebinding -force -root /

If you have this issue, copy and paste this into a Terminal window and hit return. Wait for the command to complete (you’ll get a prompt back) and reboot. This fixed the problem for me. I see the same issue is mentioned at AppleInsider but they say that no fix has been found. Perhaps I was lucky.