hi nick
overheating is nothing new in p.c,s and with components getting more and more powerful this is sure to continue to be a issue with p.c,s
however there are several inexpensive solutions to reduce the ambient tempertures and get your p.c,s tempertures down to a less worrying level
1)as allready mentioned replacing any noisy fans is a inexpensive task and will significantly reduce both the noise and tempertures,however look for some decent replacement case fans,buying a cheap fan wont help your issue and will do more harm than good
a excellent replacement case fan worth considering is the Nexus Real Silent 92mm Fan with PWM control (http://www.aria.co.uk/Products/Components/Fans%2C+Heatsinks%2C+Coolers/Case+Fans/80mm+Case+Fans/Nexus+Real+Silent+92mm+Fan+with+PWM+control+?productId=30814),this is a extremely quiet fan and has the pwm feature or " Pulse Width Modulation ",pwm fans can be attached to compatible fan controllers so you can alter the speed at which your fan spins at,so for example when you are using your p.c for general use or answers you can lower the fan speed down a bit which will still do the job it was designed for but will make less noise,a excellent and cheap fan controller worth a look at is the "Scythe Kaze Master 5.25 inch Fan Controller, Black ",this sits under your dvdrw drive and from there you have access to all your pc case fans
2)one of the worse offenders for noise in your p.c is the cpu fan and after a few years these can become noisy as the bearings begin to fail,however its relatively cheap to replace your cpu fan and heatsink,and for your p.c(socket lga775) a excellent fan and heatsink assembely is the Arctic Cooling Freezer 7 PRO (Socket LGA775) from http://www.aria.co.uk/Products/Components/Fans%2C+Heatsinks%2C+Coolers/CPU+Coolers/Arctic+Cooling+Freezer+7+PRO+%28Socket+LGA775%29+?productId=20729,this can apart from significantly reducing the noise from your p.c case can also reduce the cpu,s core temperture,for example in tests the Arctic Cooling Freezer 7 PRO has been seen to reduce your cpu temperture by up to 14°C which cant be bad
another excellent cpu cooler worth considering is the Asus Silent Knight II 3in1 Fan (http://www.aria.co.uk/Products/Components/Fans%2C+Heatsinks%2C+Coolers/CPU+Coolers/Asus+Silent+Knight+II+3in1+Fan+%28Socket+939%2C+940%2C+AM2%2C+LGA775++%29+?productId=30888),this has a strange but efficent design and also reduces your cpu tempertures significantly
3)positioning of your fans : you can put loads of fans in your pc case to keep it cool however its more important where you put them than how many you have,and a ideal pc case should have the following :
a cpu fan,1 or 2 rear 80mm case fans,a single 80mm or 120mm front case fan and a side panel fan
most pc cases have the position for the fans pre assigned however they really need to be placed with the 2 rear fans mid way up the back of the p.c and these need to draw air "out",then the front fan should be at the bottom of the front and this draws air "in"
the side panel on my p.c draws air "out" however some prefer it to draw the air in but its up to you
the main idea is to draw air in from the front and this is aimed towards the cpu and graphics card,then any circulating air will then be removed by both the side and rear fans
your power supply also plays a role in removing air from your case
however it may turn out to be cheaper to purchase a new pc case than getting all new case fan,and a excellent and cheap pc case worth considering is the excellent "Lian Li PC-7 YCF B Plus II Alu Case Black Side Window & Fan"( http://www.aria.co.uk/Products/Components/Cases/MIDI+Tower/Lian+Li+PC-7+YCF+B+Plus+II+Alu+Case+Black+Side+Window+%26+Fan+?productId=32397),this has a 120mm fan at both front and rear and a massive 250mm case fan on the side panel,this is more than enough for any p.c case,and the side fan actually spins slower than normal because of its size
theres also water cooling however this can be expensive ,but there are some reasonable water cooling kits such as the Gigabyte GH-WIU02 3D Galaxy II Liquid Cooling Kit (http://www.aria.co.uk/Products/Components/Fans%2C+Heatsinks%2C+Coolers/Water+Cooling/Gigabyte+GH-WIU02+3D+Galaxy+II+Liquid+Cooling+Kit+?productId=28251) and this actually uses non-conductive coolant which if spilt on the motherboard will just require drying out(24 hours)
i hope this helps,however any problems let me know
good luck mate !