A few family members want clean installs of Windows 7 on 3 of their computers. I have seen at the stores that there are Win 7 Home Premium "For System Builders - OEM" and Win 7 Home Premium "FULL". I understand about the legality of installing one op sys on multiple computers, but lets throw that aspect out the window for a min! lol Whats the difference between these 2 op sys's?