Dependant on your motherboard, you may have a utility you can install that provides temperature/rpm measurement on the following:
A) CPU
B) Motherboard
C) Powerfan rpm (if connected to the motherboard sensor, not typically the case)
D) Chassis fan rpm (as with C.)
There's usually cutoff presets in accordance with whatever CPU you're using that are pretty sensible. Likewise it will monitor the fan in case there's any failures there.
Although 70-75 Celcius sounds high, it should still be comfortably within the limits of the CPU (the AMD 1700 I'm using here has a thermal cutout at 86 degrees). However, it's good practice not to expose the components to more heat than necessary. This will prolongue their life and reduce the possibility of failure.
If you've got removable sides to your PC case, take one side off to stop the restricted air inside being sealed and acting as an insulator, thereby trapping the heat in. If your motherboard has a 'Qfan' or anykind of reactive fan control (i.e sets fan speed to maintain a given temp), switch it off, so that the fan runs at max speed constantly. Little noisier but allows for more efficient cooling during transient CPU temperature periods, i.e. if you've just fired up HL2 and the processor has more work to do suddenly
).
None of the above is strictly necessary as modern gear copes pretty well with warm rooms, but the bits inside will thank you.