CPU case & core temp a bit high

Hey guys.

I came here a while ago asking for some help with a build, and I got exactly what I needed. I built it a good time ago and have been using it steadily for a good time.

Anyway, out of curiosity today I decided I'd check my temperatures whilst playing bad company 2, and almost defecated in my pants when I saw the core temperatures were sitting at 100°C.

When I initially built the computer, I *think* I remember a slight confusion regarding fan speed controls and so on, but I'm not too sure whether it's just cognitive bias or not.

I'm basically here to ask whether a problem like this could be due to me not connecting the fan to a sensor or anything(it's definitely connecting and it runs and all that, measured in SpeedFan as well). Even when the CPU temperatures go up, the fan doesn't seem to speed up. It's the stock cooler, and my specs are below:

Intel i7 930(stock clocks)
Stock cooler
ASUS Rampage III Extreme motherboard
ASUS MATRIX HD5870P graphics card
Corsair XMS3 3 x 2gb RAM.
Coolermaster HAF 922 case

I have been planning on buying a noctua or some such to eventually get into overclocking, but I was under the impression my CPU was running at fine temperatures so I've been putting it on hold. My ambient temps aren't overly warm(it's cold as hell outside and I live in the northern hemisphere) so that shouldn't be it.

I'll really, really appreciate all possible advice. I can't afford another CPU for a while now and I'd rather not have my baby break on me.
Thanks in advance!