Thanks to you both for your replies. (Sorry for delay - I had quite forgotten that I'd posted on here... Oops.)
Sounds like a generally 2nd-rate machine!
Kirky, I can't remember the dismantling sequence as it was a few months ago - it is currently boxed up in the garage until I can be bothered to have another go at it! In general, it was a logical process - remove case, target the DVD drive, try and remember which screw goes back where...
I think the lens was a bit awkward to get to, but a cotton bud can get into pretty inaccessible places!
Bear in mind I had nothing to lose by taking it apart - it's a pretty useless machine in its current state...
Scoodle, February 2010