Switching hardware from one computer to another

[saechaka]

i have a friend who just fried his compaq. he currently has everything on his C: harddrive so i want to be able to switch all of his components and still be able to boot off of his original harddrive. will this be possible? can you help me find the motherboard i can buy that will let me boot from his original harddrive? i tried to use his hard drive to boot from my comp and it failed. i went and bought a 845chipset motherboard w/ddr mem. and hard drive would not boot properly. i think it uses the 845 chipset but w/pc133 but i can't seem to find out exactly. thanks for the help