Hello. I've rejuvenated an Inspiron 1000 that was left for dead. From the posts I've found, upgrading it from the stock Celeron to a P4 doesn't work because Speedstep isn't supported by the stock BIOS. It has an SIS 650 chipset, which was used in conjunction with the P4 in other laptops, so I don't think it's a chipset limitation. If it were possible to use a P4 with this laptop, that would be very nice. Stock BIOS, http://support.dell.com/support/download....aspx?c=us&cs=19&l=en&s=dhs&releaseid=R95593&SystemID=INS_CEL_1000&servicetag=&os=WW1&osl=en&deviceid=7255&devlib=0&typecnt=0&vercnt=2&catid=&impid=&formatcnt=0&libid=0&typeid=-1&dateid=-1&formatid=-1&source=-1&fileid=123827