Mass overheating

Hey there, My laptop is odd.

If I leave it on my bed on soft material, it tends to heat up to an excess of 70C...
If I put it on a hard, wooden surface that is my desk, it will reach up to 85C.

That ain't right. This is according to both Speedfan and Core Temp.
When I play games, only allowing my process power to go as high as 60%, it will overheat and shut down.
This was the case since I had it really, so I don't think it's a dust problem, although I know I shouldn't have it on my bed like that, so I do try to avoid such things.

I've ordered a little heat mat thing, but I'd like to know what's going on, and how to fix it; it can't be healthy, and I'd like to actually use my laptop at 100% as opposed to 40%

Thanks a lot!
Andy

Ps

Some details are:

Vista 32bit
3GB ram
Core 2 Duo T7500 2.2Ghz
Nvidia Geforce 8600GT (8600 something anyway)
120gb 5400rpm hard drive