You can always download hardware monitoring software from your motherboard manufacturer, or look through the BIOS setup to check, but only *if* your mobo has support for such a feature, which has been like pretty much forever, unless you have one of those retail-manufactured PC's or Dell's.
Actually I got a 'more-cramped' mid-tower case, but it has support for an exhaust and intake fan, at least. The real deal is the fact that I keep my room usually quite cold, especially during the summer with A/C. I use a cheap $8 CoolerMaster fan, however.
Generally, as power requirements go up, ambient temperature may go up as well, however, even though the P4 3.06 consumes a whopping 82W, the surface temp. is specified never to exceed 42 degrees C, and it pretty much goes for the rest of the P4's despite the intense power requirements. The earlier PII's were hot demon's as well though.