I have an ibm 300xl which supports 233/266/and 300mhz pentium 2's. However , I can only get the 233mhz pentium 2 to actually work. I have the jumpers set correctly via the motherboards own diagram and the online 300xl manual. The 266mhz p2 simply will not boot. When I install pentium 3's in it they actually also work but get limited to 400mhz and obviously are not compatible fully so within windows they are very slow. If I can figure out a way to get a 266 or 300mhz p2 to actually work with the board it would be a big help.