its very very dangerous for you computer if its over heating. It wont catch fire, computers will never get that hot, but you have to remember that teh cooler the CPU, the more efficiently (and quicker) it will run. plus the CPU will be damaged if its continually used at a higher temprature.

the best thing you can do is put in an extra case far or 2. more the computer away from confined spaces. it needs air ventalation and i'm guessing you have it hidden away between other bits of equipment or in a corner somewhere. check to make sure your existing CPU fans are well lubricated and the barrings arent worn away.

dont ignore the signs by turning off the beeping otherwise you run the risk of not having a computer at all!