The XP Project
 

Dell Latitude Cpi R400GT

400 Mhz Intel Pentium II & 256 MB RAM

It ran Windows XP okay, if you didn't have anything else and you were patient it is mostly usable.
 
Dell Latitude Cpi R400GT 1
 
Dell Latitude Cpi R400GT 2
 
Dell Latitude Cpi R400GT 3
 
Dell Latitude Cpi R400GT 4