Hi there. I had this trouble too, thought I'd snap the casing off cos it seemed glued together.
The secret is a small hole right next to the power input.
It's a bit like the hole you open an unpowered CD drive with.
You poke in a very small nail/pin/ straight paperclip, and as you do so-slide the panel that has the on/off and other buttons on it to the left, this will now pull off.
Now remove the keyboard securing screws, lift up and unclip ribbon cable. you can now get to processor-heatsink etc. HOWEVER if you want to upgrade RAM, this is done on the underside, under the cover positioned above the battery.
Hope this helps, I had to snap off the clip but it is the ONLY way to get to above parts, as well as the screen connector cables.
Best wishes all.
Bob, January 2009