I had a 5300 with a 700 in it, I bought a 1 GHZ pIII mobile and dropped it in, no problem. I would caution you that it will run even hotter then it already does, which is damn hot. Note that there 2 heatsinks that came with the 5300, ont with a heat pipe, one without, make sure yours has one. Remove the keyboard (there is a screw holding it from the bottom, the cpu will be adound the "1" "2" "q" "w" keys, remove it and take a good look at the cpu, as there are 3 types of mobile pIII's out there, you do not want to order the wrong one. I got my 1ghz for about 75 bucks on ebay. If you pull up on the heatsink it will pull the chip out of the socket, make sure you remove the 4 screws holding it down. Good luck. It was worth the effort, as it was much faster, its slow speed was 700mhz as apposed to 500, and it was plenty fast on web, and schoolwork. I did have 2 256 sticks in it I think that helped some also. Again good luck.