Bizarre keyboard problem - middle row keys (asdfghjkl) won't work

Hi guys

I hope somebody can help me here. We have a Macbook 2ghz with Mac OSX 10.4.11 and for some bizarre reason, the middle row of keys have stopped working. It's only keys A,S,D,F,G,H,J,K,L - all other keys work as normal.
The keys will randomly start working again on occasions, but the majority of the time they do not. However, if pressure is applied to the mousepad, they work!

We noticed that another user (cmkrb) also had the same problem with his/her macbook and the thread said that he/she was going to take it to Tekserve, which I believe to be a Mac specialist in the US. I could not post in that thread as it was archived and I have no way of contacting cmkrb to find out what the outcome was, so I'm hoping that he/she reads this and lets me know.

We did a clean re-install of the OS as one of the latest security updates caused problems to the system and we hoped that this might have rectified the keyboard issue, but alas no.

I'd appreciate it if your (much appreciated) replies are not too (Mac) jargonised or technical as I have to admit that I'm a PC man and have very little experience of Mac's and their hardware/software. I'm fairly competent at troubleshooting/building a PC so I'm no idiot but put a mac in front of me and I'm out of my comfort zone!

Once again, we sincerely appreciate any help or advice that you may throw our way, even if it's only 'take it to the Apple Store'!

Cheers guys

Michael & Rosie