I had had the same problem and tried all the suggested answers here without effect.
The one answer I haven't seen, here or elsewhere, which did work was to update the BIOS.
The keyboard problem appeared after I had cleaned out and reinstalled XP and installed Microsoft Office 2007 on an IBM laptop Z60m.
A superb techie spent three hours trying to find the answer. He found most of the answers suggested here, plus several others, including a Microsoft statement "recognizing the problem." Eventually, he tried updating the BIOS, which worked. But he thought of that himself. Nowhere did he find anything suggesting updating the BIOS.