They are quite easily replaced, I would advise to get one with power
rating or Wattage equal to or more than the one you are replacing.
Supposing its a 300 watt PSU and you replaced it with a 400 Watt
unit.
The 400 Watt unit would not draw any more power than the 300 Watt,
being a higher rating it would run cooler and would have an easier
life as it is not working at full capacity.
Here is a link that may be useful, from memory you click at the link
near the bottom that say's 'Check Now' (or similar to that and it'll
calculate the minimum Wattage you'll need.
http://www.journeysystems.com/power_...calculator.php
Ensure the computer is unplugged for at least 5 minutes and it's just
a matter of pressing the locking tab before removing the plug from
the mobo. PSU's normally comes with a 4 pin plug that isn't used on
AMD's CPUs but the Pentium chips require this extra 12V 4 pin plug on
the mobo, any unused plug's just coil up and tuck safely away. The
unit is usually held in with four screws at the back.
Do not attempt to pull the plug from the mobo without
pressing the locking tab
There are good makes and some poor ones.... a good clue is the weight,
the heavier the better the best ones are Enermax and Antec brands....
stay well clear of the 'El Cheapos', paying as much as you can for
one may be a good policy.
Davy