I want to upgrade it from 675mhz or so
The only 675MHz CPU I could find on Google was a Sparc64
Keep in mind few older laptops will recognize hard drives over 32GB, and that workarounds are usually neither elegant nor reliable.
IMHO upgrades beyond a 20-30GB HD and 256/512MB RAM are not worth it for vintage machines.
P1 laptops are doomed by nonstandard RAM, an 8.4GB HD limitation, and a different mounting pattern for HD's.