Call Gateway. or go to their sight, just look up the model number of you computer. They usually display their motherboard manufacturers.
You can always tell them you need a bios update file and they will tell you which motherboard it is., then you can ask them what the highest processor it can handle. They may suggest a bios update anyway to get a higher multiplyer, as newer processors are created, they have a higher multipler and often support it through a bios update.