The highest level CPU that can be used depends on the bios. If the manufacturer continued the product to the end of that life cycle then technically you could use the fastest CPU for the socket type. looks like that foxconn is a Socket 478. I would suggest going with one of the new slim line/book bare bone computers as apposed to messing with all of this legacy technology. It's just a suggestion.
thanks for your help everyone, is there any software which ca help me find compatible processors? im not a IT professional of any sort, so somethings are bit hard to understand. thanks again!
You can always download CPU-Z that should give you some idea of what hardware is installed. The real question is: where are you going to get the "new" hardware from? Most retailers don't stock these legacy CPU's anymore, and those that do will charge you more than they are worth. As the other posters I too am unable to find specific information about the motherboard installed so I can only guess what CPUs are supported. Since it is clocked at 1.8 ghz I would guess it is either a socket 754 or 638, in any case the highest upgrade CPU available would be a 2ghz processor. The benefits from upgrading would be almost null.
Most of the time for hardware this old, it is cheaper to just buy a new cheap system for $300 which will have twice the performance of your old computer.
thanks Supermuncher85 , great response! thats just what i was looking for!