A watt is a watt is a watt. No matter how much juice you feed a component, it is only able to draw so many amps/watts. Take a look at your powersupply, how many watts is it rated at? If you have a 250-300 watt powersupply, you would need a 300 watt inverter. While you might be able to get by with a lower watt inverter, the "start up" surge of powering up your system might be beyond what the inverter is capable of handling. Remember, a watt is a watt, and an amp is an amp...

el-jefe